A child launches a toy rocket in the air, and the function f(x) = -10x +90x+ 20 represents the flight of the rocket, where x

A child launches a toy rocket in the air, and the function f(x) = -10x² +90x+ 20 represents the flight of the rocket, where x is the time in seconds and f(x) is the height (in feet) at x seconds. a. For how many seconds is the rocket higher than 100 feet above the ground? b. Explain how you found your answer.