Answer is 34 ft
Step by step
We can find the diagonal of the right triangles using Pythagorean theorem a^2 + b^2 = c^2
We know the base is 15 less 9 = 6, divided by 2 triangle bases = 3 for each base and height is 4
3^2 + 4^2 = c^2
9 + 16 = c^2
25 = c^2
√25 = c^2
c = 5
Since the right triangle diagonals are equal they are both 5 ft
Now we can add the 4 sides together to get the perimeter
15 + 9 + 5 + 5 = 34 ft