How do I solve this math problem?

Question

How many sec. for it to hit the ground using h=480-16t^2

Answer 1

 I t to the hit the  ground

Make h= 0.

0 = 480 - 16t²

Factor.

0 = 16(30 - t²)

Set each by zero and solve for t.

30 - t² = 0

-t² = -30

t² = 30

t = √30 seconds.

Answer 2

h = 480 - 16t^2

Substitute h = 0 since height will be zero when hit the ground.

0 = 480 - 16t^2

480 = 16t^2

divide each side by 16

480/16 = t^2

t^2 = 30

t = sqrt (30)

t = 5.4777 seconds