The formula in computing the area of the triangle is:
A = bh/2
Where A = area of the triangle
b = base of the triangle
h = height of the triangle
What is asked in the problem is the height of the triangle and you are already given the area so you substitute the given measurements to the formula:
64 = 8(h) / 2
2 (64) = 8h
8h = 128
h = 16
Therefore, the height of the signal flag is 16 in