It turns out that the ratio of football to volleyball is 7: 3, with 20 * * *, which means there is 7/ 10 X 20 football, which is 14 volleyball.

After buying football, the total is 20+X, football is 14+x, volleyball is 6, (14+x): (20+x) = 4: 5, so X= 10. 5( 14+X)= 4(20+X)70+5X = 80+4X X = 10