Answer:
2.05hrs
Step-by-step explanation:
Given he total cost c(x) of hiring a dump truck and an operator is described by the function c(x)=300+31x-3.90x^2 , where x is the number of hours worked. If c(x)=$220, then;
220 = 300+31x-3.90x^2
300+31x-3.90x^2 - 220 = 0
3.90x^2 + 31x - 80 = 0
x = -31±√31²-4(-80)(3.9)/2(3.9)
x = -31±√961+1.248/7.8
x = -31±47/7.8
x = -31+47/7.8
x = 16/7.8
x = 2.05
hence the number of working hours is 2.05hrs
