Answer:
X=8
Explanation:
Given that the Area is 36ft^2, and the formula for calculating the area of a triange is:

we have:

we can start solving for x through the quadratic formula, but that will take long.
Instead, we can try replacing x by some numbers.


After a while,

We find that x=8.
IMPORTANT: X can also be -9 in this case. But a negative measurement doesn't make sense in this context, I would say that x=8 in this problem.