Exponential growth problem

Ok me and my friend are trying to determine the function used on an online game.

When you build a level 1 metal mine, your production goes up to 22 metal and hour.

level 2 is 48

as i said before we are trying to find the exact function that is used, and i am having problems trying to do this, i think it has to do with the rate. i did plot a graph and it shows that it increases less as approaches infinity.

It doesnt sound that hard, i should be able to do it, though i cant remember how :S

Here are a table of values

lvl p/h

1 22

2 48

3 79

4 117

5 161

6 212

7 272

8 342

9 424

10 518

thanks