I would recommend eliminating the variable 's' because one of the 's' variables in the system is negative. So now, what is the least common multiple of 2 and 3? Keeping that in mind, multiply each equation by the "missing factor" in the least common multiple. Next, add the two equations together; if you did everything correctly, the 's' variable should drop out and you'll be left with something of the form which is relatively simple to solve. Lastly, now that you know 'r', you can plug it into either equation to find 's'.

I hope you can make sense of this. Please post back if you have further difficulties.