Perimeter is the sum of all outside dimensions.
Solve for x first:
12 + x+7 + x+2 + 5 + x +4 + x + 4 = 42
Combine like terms:
4x + 34 = 42
Subtract 34 from both sides:
4x = 8
Divide both sides by 4:
X = 2
Now solve for EF by replacing x:
EF =. X + 7 = 2 + 7 = 9 feet.
