A math question PLZ HELP ASAP!!

Question

A pebble is thrown into the air from ground level with an initial velocity of 20 feet per second . The height of the pebble h any given time can be described by the equation

h = - 16t ^ 2 + 20t

Find the time at which the height of the pebble is 4 feet . Round your answer to the hundredths place

Answer 1

h = -16t² + 20t

We want to know the value of t that gives us h = 4.

4 = -16t² + 20t

We can rewrite this in quadratic form.

16t² - 20t + 4 = 0

Here, we can use the quadratic formula.

a = 16

b = -20

c = 4

t = (20 ± √(20² - 4(16)(4)))/2(16)

t = (20 ± √(400 - 256))/32

t = (20 ± √(144))/32

t = (20 ± 12)/32

t = 0.25, 1 seconds