The quadratic function
d=-9x² + 40 models a
skateboarder's distance, in
feet, from the bottom of a hill
x seconds after the skateboarder
starts moving down the hill.
After how many seconds is the
skateboarder 4 ft from the
bottom of the hill?

A) 3s B) 4s C) 2s D) 3.5s

Please help!! Also if you could explain that would be great! Tysm!