Question

Use addition or substitution to find the value of x for this set of equations.
x - y = 120
x + y = 150

Answer 1

Addition is the easier way to solve for x here, but substitution would work as well.

For addition, since we know the values for x and y that satisfy these equations work for both, we can add the two equations and keep the equality. So, take the vertical sum:
x+x-y+y=120+150,
which simplifies to:
2x=270.
Dividing by 2:
x=135.

Incidentally, y =15.