The perimeter of a rectangle is __________. 

The correct answer is: P = 2(l + b) 

TO FIND-
Perimeter of a rectangle.
SOLUTION-
We know that a rectangle has 2 pairs of equal sides.
Also, Perimeter of any polygon = sum of the length of all its sides.
∴ Perimeter of a rectangle = 2 length + 2 breadth
∴ Perimeter of a rectangle = 2 (Length + breadth) ........... (Taking 2 common)
∴ Perimeter of a rectangle = 2 (l + b)
FINAL ANSWER-
Option 'a' i.e. 'P = 2(l + b)' is the correct answer to the given question.