First what we gonna do is solve for y.
x+5y=28 Subtract 5y both sides.
-5y -5y
x=-5y+28 Then you have to replace x with the equation.
2(-5y+28)+3y=21 Multiply.
-10y+56+3y=21 Combine like terms and subtract 56 both sides.
-56 -56
-7y=-35 Divide -7 both sides.
y=5 Simplify.
x=-5(5)+28 Multiply and add.
x=-25+28
x=3
Heres your answer x=3 and y=5.
