What was the weight of the silicon when the phosphorus weighed only 12 kilograms?

Question

The weight of the silicon varied directly as the weight of the phosphorus. When the silicon weighed 400 kilograms, the phosphorus weighed 100 kilograms. What was the weight of the silicon when the phosphorus weighed only 12 kilograms?

Answer 1

Weight of Silicon/Weight of P = k = 400/100 = 4

x/12 = 4, so x=48 kgr