Question 10610
We be able to substitute y = 2x to x + y = 12:
x + y = 12 ----- x + 2x = 12
                     3x = 12
                      x = 12 : 3
                      x = 4
Then, y = 2x ------ y = 2(4) = 8
so, we find x = 4 and y = 8