The triangle has an area of answer choice D, 16.4 units
We know that the equation for a triangle is 1/2 b*h
We also know that 8 is the height of the triangle, so the variable missing is the base.
Using the Pythagorean theorem, (a^2+b^2=c^2), we can find the length on the missing side.
8^2+x^2=9^2
64+x^2=81
x^2=17
Square root 17 equals 4.123, so therefore the base is about 4.1 units.
(4.1*8)/2 = 16.4