Step-by-step explanation:
3x=28+y
x=28+y÷3
then puttingx=28+y÷3
3x=14+y
3(28+y÷3)+y=14
84+3y+3y=42
3y+3y=42-84
y=-42÷6
y=7
so putting y=-7
3x-y=28
3x-7=38
x=38+7÷3
x=15
