To make concrete it take 8 parts crushed gravel, 7 parts water and 5 parts cement mix. a worker needs to make 220 kg of concrete. how much gravel, water and cement mix is needed.

A complete load of concrete = 8 parts gravel + 7 parts water + 5 parts cement.

Total number of parts in every load = 8 + 7 + 5 = 20 parts

If total load = 220 kg, then       20 parts = 220 kg

Divide each side by  20 :             1 part = 11 kg

gravel   = 8 parts = 8 x 11 kg = 88 kg
water    = 7 parts = 7 x 11 kg = 77 kg
cement = 5 parts = 5 x 11 kg = 55 kg

Check:    88 + 77 + 55 = 220         yay !

X=y+4 is the answe