OK, i have two data sets, one is an Input, one is an output

As the Input Grows, the output grows at a faster rate

EG

at 225 the output is 18.92 or 8.41% of the Input

at 254.25 the output is 23.31 or 9.17% of the Input

it keeps on like this until you reach

355 input with an output of 38.5 or 10.83%

How would i go about finding the a formula to solve for the unknown?

Thanks for the Help

Kevin