From the meaning of the question: 3x-x-(x+21) =1/5× [x+(x+21)]-3.
x-2 1 = 1/5×[2x+2 1]-3
x-2 1=(2/5)x+2 1/5-3
x-2 1=(2/5)x+6/5
3/5x= 1 1 1/5
x= 1 1 1/5×5/3
x=37
Then 3x= 1 1 1
So * * *11/classmates won the prize.