A falling rock: A rock is thrown downward, and the distance D, in feet, that it falls in t seconds is given by D = 16t 2 + 3t. Find how long it takes for the rock to fall 400 feet by using a. the...

A falling rock: A rock is thrown downward, and the distance D, in feet, that it falls in t seconds is given by D = 16t 2 + 3t. Find how long it takes for the rock to fall 400 feet by using a. the quadratic formula. b. the crossing-graphs method.