the slant height would be the hypotenuse of a right triangle. 1/2 the length of the base would be one side of a right triangle. Use the Pythagorean theorem to find the height:
89.9^2 = 9.9^2 + x ^2
8082.01 = 98.01 + x^2
X^2 = 8082.01-98.01
X^2 = 7984
X = sqrt(7984)
X = 89.35
Round to 89.4
