Working on the assumption that in making the program 90 times faster, a speed up of 90 was yielded;
We can apply the speed up formula.
1/ [(1 - percentage of time) + (percentage of time / speed up achieved by percentage) ]
Applying this to your problem variables;
Speed up = 1 / [ (1 - 0.1) + (0.1 / 90) ] = 1.112
Leave a comment below if you need some more clarification. Cheers!