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

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)

2 (x-3) + 2 (4) = 40

2x-6+8=40

2x+2=40

2x=38

x=19

Length = (x-3) = (19-3) = 16 cm