Question

A rectangle has length (x-3) cm and width 4 cm. The perimeter of the rectangle is 40 cm. Find the length.

Answer 1

2(x-3)+2(4)=40
2x-6+8=40
2x+2=40
2x=38
x=19
Length=(x-3)=(19-3)=16 cm

Answer 2

we actually don't need to solve for x, just legnth

P=2(L+W)
40=P
L=x-3=L (since we are solving for Legnth not specifically x)
W=4

40=2(L+4)
divide both sides by 2
20=L+4
minus 4 both sides
16=L

legnth=16 cm (x=19 just fyi)