Assuming this is a system of equations, here is how to find x.
2x + 3y = 45
x + y = 10
Multiply x + y = 10 by 2 so you are able to use the elimination method.
2x + 3y = 45
2x + 2y = 20
Subtract.
y = 25
Now that we've found y, we can plug it in to find x.
x + 25 = 10
Subtract 25 from both sides.
x = -15