Isolate one of the variables x + 4y = 21 subtract 4y from both sides x = -4y + 21
Plug that into the other equation 4x - y = 16 4(-4y + 21) - y = 16 -16y + 84 - y = 16 combine like terms -17y + 84 = 16 subtract 84 from both sides -17y = -68 divide both sides by -17 y = 4
Plug that into the equation x+4y=21 x + 4(4) = 21 x + 16 = 21 subtract 16 from both sides x = 5
