The lenght = 2 x + 3
and the width = 3x - 4
the perimeter = 78 feet
So, 2 [ (2x + 3) + (3x - 4) ] = 78
2x + 3 + 3x - 4 = 39
5x - 1 = 39
5x = 39 + 1
5x = 40
x = 40/5 = 8
so,
The length = 2 x + 3 = 2 * 8 + 3 = 19
and the width = 3x - 4 = 3 * 8 - 4 = 24 - 4 = 20
So, the dimentions are 19 feet and 20 feet