The first equation is already solved for y. So we can plug that into the second equation.
3y - x + 5 = 0
3(-2x + 10) - x + 5 = 0
Distribute the 3
-6x + 30 - x + 5 = 0
Combine like terms
-6x - x + 30 + 5 = 0
-7x + 35 = 0
Subtract 35
-7x = -35
Divide by -7
x = 5
Plug x into either equation to solve for y
y = -2x + 10
y = -2(5) + 10
y = -10 + 10
y = 0
