Let x be fast, the skin is 5 sides and 70-X is 6 sides.

12X/ 12 = 15(70-X)/20

7X=2 10

X=30

70-30=40 is greater than 30.

So we should make 30 soccer balls, use 30 large skins to make pentagons and 40 large skins to make hexagons.