For this equation, you'll need to set x to 0 and solve from there.
[tex] y=-16(0-1)^2+21 [/tex]
First step is to solve the parentheses and then square the answer. Your equation will look like this: [tex] y=-16*1+21 [/tex]
Next, you will multiply -16 and 1, and then add the product of that by 21. Your answer will be [tex] y=5 [/tex]
In short, the ball is thrown from 5 feet above ground.
