Solve the following system using substitution x+4y=21 4x-y=16

x+4y=21
4x-y=16

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

Hope this helps!