posted by Tina .
A person standing near the edge of a cliff 120 feet above a lake throws a rock upward with an initial speed of 40 feet per second. The height of the rock above the lake at the bottom of the cliff is a function of time and is described by the function H(t) = –16t2 + 40t + 120.
a) How many seconds will it take until the rock reaches its maximum height?
b) What is that height?