C(t)=26t^2+168t+4208, and we wish to know when C(t)=15000
26t^2+168t+4208=15000
26t^2+168t-10792=0
They want you to use the quadratic formula...
For a quadratic of the form ax^2+bx+c=0, the quadratic formula is:
x=(-b±√(b^2-4ac))/(2a), in this case we have:
x=(-168±√1122368)/52, since x>0
x≈17.14
1958+17.14≈1975.14
So by 1976 the number of new cars will reach 15000.
