First, put them directly above each other.
5a+2s=48
3a+2s=32
You need to combine these, but in order to do so, we want to get rid of one of the letters. The S's line up very well, and all we need to do is multiply the bottom equation by a negative 1. This will look like this,
-3a-2s=-32 (and add it to the other equation)
5a+2s=48
This gives you
2a=16
Divide both sides by 2 to get a by itself.
a=8, is your answer!
If it asked for s, you would put 8 into whichever equation seems easier for you, and then its just simple crunching it out.
Hope this helped!