30 kg of mixed sugar consisting of four kinds of sugar, namely milk candy, fruit candy, soft candy and crisp candy, wherein the sum of the mass of milk candy and fruit candy accounts for 2/3 of the total mass; The sum of the mass of milk candy and soft candy accounts for 3/5 of the total mass; The sum of the mass of milk sugar and crisp sugar accounts for 75% of the total mass. How many kilograms are there in each of these four kinds of sugar?

Answer: The sum of the mass of milk candy and fruit candy: 30x2/3 = 20kg (1).

The sum of the mass of milk candy and soft candy: 30x3/5 = 18kg (2)

Sum of mass of toffee and shortbread: 30x75% = 22.5kg (3)

We found that (1)+(2)+(3) is: 3x milk candy quality+fruit candy quality+soft candy quality+crisp candy quality = 20+18+22.5 = 60.5kg.

There is also 30 kg of mixed sugar composed of four kinds of sugar: toffee, fruit candy, soft candy and crisp candy, so toffee: (60.5-30)/2= 15.25 kg.

So fruit candy: 20- 15.25=4.75 kg. Soft candy:18-15.25 = 2.75kg.

Crispy sugar: 22.5-15.25 = 7.25kg.