the answer would be 320. all you have to do is set up a proportion.
that looks like 15 over 100 and 48 over n ( n is the number we don't know yet )
and cross multiply to get; 15n and 100*48=4800
now you would have to divide both 15 and 4800 by 15
to get; 15n/15=n and 4800/15=320
so you would get n=320