f(x)=0.485x2-1.694x+0.315.
Given: f(6) is the millions of users in 1996 and f(7) is that in 1997, we can deduce that x=year-1990.
When f(x)=127:
0.485x2-1.694x+0.315=127,
0.485x2-1.694x-126.685=0.
Use quadratic formula to solve:
x=(1.694±√(1.6942+√245.7689)/0.97,
x=18 approx. (We reject the negative solution because we are predicting a future (positive) value.)
So in 1990+18=year 2008, the estimated number of users reaches 127 million.
As an addendum, the 1996 number was about 7.61 million and that for 1997 was about 12.22 million users.