Answer
perimeter is $40\frac{2}{3}$ ft
Work Step by Step
The combined lengths of the 2 segments at the top equals the length of the bottom side.
$3x+7=12$
$3x+7-7=12-7$
$3x=5$
$x=\frac{5}{3}$
The perimeter is:
$12+12+5(\frac{5}{3})+5(\frac{5}{3})= 24+\frac{50}{3}=24+16\frac{2}{3}=40\frac{2}{3}$
