lets say that we want to eliminate x from the equation.
from (1): 3x-4y=11 15x-20y=55 — (3)
from (2): 5x+6y=12 15x+18y=36 — (4)
( make 15x the common variable ) so, ( 3 ) - ( 4 ) : ( 15x -20y ) - ( 15x+18y ) = 55 - 36 15x - 20y - 15x + 18y = 19 -2y = 19 -y = 9.5 y = -9.5 now that we know the value of y, sub y = -9.5 into (1) 3x - 4(-9.5) = 11 3x + 38 = 11 3x = 11 - 38 x = -9
