If the water fee is X yuan, the porridge bill is 4x yuan and the milk bill is 48x yuan.

Meaning from the title: 5x +32x +48x =68.

Solution: x =0.8, 4x =3.2, 48x =38.4.

So the water list is 0.8 yuan, the porridge list is 3.2 yuan, and the milk list is 38.4 yuan.

The second question:

Understand: Other substances remain unchanged.

700 * (1-0.97)/(1-0.93) = 300 kg.