I used the equations:
C+H+S=100
10C+H/16+S=100
Since you have two equations, three unknowns, you have to choose one of those variables and assign it a value. I assigned different values for H because there are only 6 possibilities: 16, 32, 48, 64, 80, and 96. Just by plugging in each of those values and running with it, you can see there is only one answer that fits the bill.