The value of h, if perimeter is 87 cm is ____________. 

The correct answer is: 34 cm

The perimeter is the sum of all the sides of a polygon.
In this question we are given the perimeter of of the polygon and we have given  sides of this shape and we have to find the  side by using the perimeter of the polygon given.
Step1: Calculating the sum of the given sides.
The  given are ,  and 
Sum =
=>
Step2: Subtracting the sum from the perimeter of the given figure.
side h = 
h=
=> .
So, the value of h is .