I dont understand math

Question

A projectile is launched from ground level with an initial velocity of v₀ feet per second. Neglecting air​ resistance, its height in feet t seconds after launch is given by s = -16 t ² + v₀ t. Find the​ time(s) that the projectile will​ (a) reach a height of 64 ft and​ (b) return to the ground when v₀ = 80 feet per second.

Answer 1

s = 64 ft; v₀ = 80 ft/s, t = time to 64 ft

64 = -16t² + 80t rearranged is 16t² - 80t + 64 = 0

divide by 16 to get t² - 5t + 4 = 0

factor to get (t - 4) x (t - 1) = 0 so t = 4 or 1 sec (1 sec is unrealistic so the answer is 4 sec for part a

it takes the same number of seconds to return to the ground so the answer to part b is 8 sec