Given that
x + 6y = 9---------1
and
-x + 2y = - 15------- 2
Make x subject of formula in both equations
From equation 1
x = 9 - 6y
From equation 2
2y = -15 + x
2y + 15 = x
x = 2y + 15
Equating the two equations
2y + 15 = 9 - 6y
collect like terms
2y + 6y = 9 - 15
8y = -6
