This is a system of equations and in this you see there is 3x and negative three x. To solve this you need tp get rid of one of the variables. so we can add the two equations together to get 3y=6. This means that y=2 if we divide by 3 on both sides. Then we just plug 3 in for y and we get 3x+10=7. We subtract 10 on both sides to get 2x=-3 which means x=-1.
