To solve a system of equations, you can use elimination, substitution, or graphing to find an intercept.
I am going to use substitution, where you convert one variable to another, and then substitute that expression for the original variable in one of the equations.
For example, here, the x equivalent for the variable y is already given (actually twice). We know that y = 2x + 7. That means you can replace the y in the second equation with (2x + 7).
So when you do that, you get the equation:
2x + 7 = -x - 8
To solve for x, get the xs to one side and the numbers to another by adding x to both sides and subtracting 7 from both sides, to get the equation:
3x = -15
Then divide both sides by 3 to get x = -5.
Now that we know x, we can return to the original equation to find y. Since y = 2x + 7, now you could say y = 2(-5) + 7, which simplifies to -10 + 7, which is 3.
So y = -5 and x = 3.