How do I express the answer graphically and algebraically?

Question

A motorcycle stunt rider jumped over the canyon. The path of her motorcycle was given approximately by the function H(x)=−0.005x^2+4.2x+900, where H is measured in feet above the ground and x is the horizontal distance from the launch ramp. 

B) What was the rider’s maximum height above the ground, and how far horizontally was the rider from the ramp when she reached the maximum height?

Answer 1

Convert the function to vertex form.