Question 348273
N=4x^2 + 5x +1


So they're telling you that N=85 because it says N is in thousands. You need to solve for x. Whatever number you get for x, add that to 1990 and you will find the year.


N=4x^2 + 5x +1
85=4x^2 +5x + 1
0 = 4x^2 + 5x -84


You now have a quadratic equation. You can solve this using the quadratic formula.


{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}


Where a = 4, b = 5 and c = -84


After doing the algebra for the quadratic formula (or using an online solver), you will find that there are two answers:


x = -5.25 or x = 4


Choose the positive answer, x=4, because it wouldn't make sense to be negative.


That means that there were 85,000 computers in this city in 1994.


Hope this helps!