Question

px + qy = r
2px - qy = 2r
When solving this system of equations, x =

Answer 1

px + qy = r
2px - qy = 2r
----------------add
3px = 3r

x = 3r/3p
x = r/p

Answer 2

You just add the equations:
  px + qy = r
2px  - qy = 2r
3px = 3r
divide by 3
px = r
divide by p
x = (r)/(p)