Since, finding the Perimeter of a Rectangle = 2L + 2W,
and the Perimeter of 34 ft is given, then 34 ft - 2(7 ft) = 34 ft - 14 ft = 20 ft divided by 4 sides = 5 ft. which is the width.
To get the measure of the length, 5 ft + 7 ft (longer than the width) = 12 ft