Math equation needed for complicated problem?

I am editing a movie with footage that was given to me. The audio is slightly slower than the visual and it is very long, so by the end the difference is quite severe. I need an equation to figure out by what % to increase it's speed. although I do not know if all will be needed in the equation the variables I have are: 1. the frames per second that the footage (v and a) is running at (it is the same for both v and a) 2. the length of the clip 3. how many frames the audio is behind at the end when aligned correctly at the beginning. (I already tried 102% and that extra 2% was a lot too much so it will most likely be a decimal number after 100%) So if you could send me an equation for that I can put in the numbers and solve it myself. Thanks!