A large explosion

Question

A large explosion causes wood and metal debris to rise vertically into the air with an initial velocity of 112 feet per second. The function

h(t)=112t-16t^2

gives the height of the falling debris above the ground, in feet,  seconds after the explosion.

A) Use the given function to find the height of the debris 4 second(s) after the explosion:

B) How many seconds after the explosion will the debris hit the ground?

Please explain step by step, my teacher is no help

Answer 1

h(4) = 112(4) - (16)(4²)

0 = 112t - 16t²

0 = t(112 - 16t)

t = 0 or t = 7