Step-by-step explanation:
First, draw a parallelogram and label the sides with the dimensions L, S=9, L, and S=9. [note: opposite sides of a parallelogram are of equal lengths]
The problem statement tells us the value of P [the distance around] = perimeter = 48 = L + 9 + L + 9.
48 = 2L + 18
30 = 2L [subtract 18 from both sides]
15 = L [divide both sides by 2]
Check: If L=15 and S=9, what is P?
P = 15 + 9 + 15 + 9
P = 48 [that checks!]
