Answer
9 seconds
Work Step by Step
h(t)=-16t^2+80t+576
factor -16(t^2-5t-36)
Using ac method, find two numbers whose products are -36 and their sums are -5. The numbers are -9 and 4.
t^2-9t+4t-36
t(t-9)+4(t-9)
(t+4)(t-9)
t+4=0 t=-4 does not make sense
t-9=0 t=9
After 9 seconds the object strikes the ground.
