i don't know how to do this problem

Hi Alex;

width...x

length...7x+3

perimeter=2(length+width)

54=2(x+7x+3)

54=2(8x+3)

54=16x+6

Subtract 6 from both sides...

54-6=16x+6-6

48=16x

Divide both sides by 16...

48/16=(16x)/16

3=x

**width....3**

**length...**[(7)(3)]+3=21+3=

**24**

Let's check our work...

perimeter=2(length+width)

54=2(3+24)

54=2(27)

54=54