When asked to solve by elimination, you put them on top of one another, like you're going to add it.
10x + 7y = 9
-4x - 7y = 9
See that 7y? You can cancel those out because one is negative, and one is positive. So those are gone. You finish adding the rest of the numbers as usual and solve for x.
6x = 18
x = 3
Take x, and plug it into either equation to find y.
