Write a function rule for the area of a triangle with a base 3 cm greater than 5 times its height. what is the area of the triangle when its height is 6 cm?

Let the height be x, then base = 5x + 3
Area = 1/2 x base x height = 1/2 x(5x + 3) = 5/2 x^2 + 3/2 x
f(x) = 5/2 x^2 + 3/2 x

for x = 6 cm
Area = 5/2 (6)^2 + 3/2 (6) = 5/2 (36) + 9 = 90 + 9 = 99 cm^2