Question

the function d(t)=15t^2-100t gives the distance a car going a certain speed will skid in t seconds. find the time it would take for the car to skid 170 feet

Answer 1

15t^2 - 100t = 170
15t^2 - 100t - 170 = 0

3t^2 - 20t - 34 = 0

solve for t

t = [-(-20) +/- sqrt( 400 - 4*3 *(-34) ] / 6

= 8.07 seconds

Answer 2

Equate 170 feet to d(t) = 15t^2 - 100t.  Rearrange these 3 terms in descending order according to the powers of t.  Then solve for t.  Use the quadratic formula or some other suitable approach.