Question 604177
-5x-2y=21 
y=2x+6


substitute y=2x + 6 into the first equation:
-5x - 2*(2x+6) = 21
-5x - 4x - 12 = 21
-9x - 12 = 21
-9x = 21 + 12
-9x = 33
x = 33/-9 = -11/3


y = 2x + 6 = 2*(-11/3) + 6 = -22/3 + 6 = -22/3 + 18/3 = -4/3


so the solution is:
x = -11/3
y = -4/3