Well, here it is the solution:
Perimeter = 12 + 6 + 14 = 32 ft
Now we replace it into the A, and we will have:
A = ~32(32-14)(32-12)(32-6) = ~299520 = 547.28
The same A can be written as (b*h)/2, so:
A=(base*height)/2
547.28 = (14*h)/2
14*h=547.28*2
h=547.28 * 2 / 14
h=78.18
Rounded to 78
