This function is nonlinear because,

Bob has $150 in his savings account and saves $40 per month. Which function models his savings?

Mr. Harris attaches a full tank of propane to his grill. Then he turns on the grill and cooks food for a barbecue. Which graph shows the relationship between the amount of propane in the tank and time?

Correct option is (b).
At time 0 minute the tank was full
Then Mr Harris coooked which will bring down the level of propane in the tank with passage of time and clearly in option (b) the graph is dowanward means with the passage of time the level of propane is getting down

The value of a stock decreases sharply for 2 weeks, then increases sharply for 1 week, and then decreases sharply again for 2 weeks. Which graph shows the relationship between the value of the stock and time?

Correct option is (d).

This function is linear because,

Correct option is (a).
when x is 0,y is 2
when x is 2 ,y is 8
when x is 4,y is 14
both the entities are changing with constant rate
therefor the graph will be linear.

Identify the slope of the equation,
y = -3x + 4

The graph shows how a motorboat travels around a lake. What does the graph most likely show?

in sufficient data .
But the graph clearly depicts the boat is at  moving with increasing speed for few minutes and then it gets constant speed

Mr. Z is starting his own car club, there is a $30 join up fee and a $5 monthly fee. The rate of change/ slope is _______________.

Identify the equation of the line in general form when the slope is 0.6, and the y-intercept is 0.4

Chris can earn money per hour for his work. How much will he earn in 6 hours? 

In this question, To find the total money earned by Chris, we have find the how he would earn in each specific hour and for total 6 hour we just add the all money of each hour.

Identify the number of intervals in the below graph.

In this question, to find intervals we have to find where the graph just discontinued. And as long as graph is continuous and this is interval of this graph.

John drained the water in his tub. The amount of water left in the tub (in liters) as a function of time (in minutes) is graphed.

How much water is getting drained in 2.5 minutes?

In that same question we can also fine the how much amount of water remove at any minutes by finding water drained at one minutes 360/5=72. Which leads to us to find the water drained at any given minutes by multiplying in it.

Identify the statement that best describes the increasing and decreasing of the graph.

You can apply same kind of method to find the intervals of the graph or function given in graph is increasing or decreasing at a point.

Is the given function increasing, decreasing or constant?

We can also find out the function is decreasing by looking at its line or curve or if the function is given the we must find first derivative if it was.

John drained the water in his tub. The amount of water left in the tub (in liters) as a function of time (in minutes) is graphed.

How much water is getting drained in five minutes?

In that same question we can also fine the how much amount of water remove in one minutes by 360/5=72. Which leads to us to find the water drained at any given minutes by multiplying in it.

Look at the graph below and identify whether the function at interval 3 is increasing, decreasing or constant.

You can apply can process throughout any question related to increasing, decreasing and constant interval where you can find out easily by looking the graph or slope of line.