Question

The formula for the perimeter of a rectangle is P = 2l + 2w. The length of a rectangle is 7 units longer than its width.

Answer 1

The expression to represent the perimeter of the rectangle is:
2(w + 7) + 2w

Answer 2

$P=2l+2w$
if
$l=w+7$
we can plug this expression for the length into the first equation and get:
$P=2(w+7)+2w=4w+14=2(2w+7)$