Question 62881
Y=3X THEN SUBSTITUTING (3X) FOR Y WE GET
X+2*3X=-21
X+6X=-21
7X=-21
X=-21/7
X=-3
Y=3*-3
Y=-9
PROOF
-3+2Y=-21
-3+2Y=-21
2Y=-21+3
2Y=-18
Y=-18/2
Y=-9
PROOF
-9=3*-3
-9=-9