Question

What is the length of the base of a triangle with height 18 m and area 99 square m?

Answer 1

Use the equation for the area of a triangle:
$A = \frac{1}{2} hb$
where A = area, h = height of the triangle, and b = base of the triangle.

You know that h=18m and A=99$m^{2}$. Plug those values into the equation and solve for b, the base.
$A = \frac{1}{2} hb \\ 99 = \frac{1}{2} (18)b \\ 99=9b\\ b=11$

The base is 11m long. 

Answer 2

Use the area formula and solve for height.

Area of triangle = 1/2(b)(h)

99 = 1/2(b)(18)
99 = 9b
11 = b

Hope this helps :)