a) To make sherbet, 11 parts juice, 4 parts cream and 1 part sugar are used. How many kilograms of cream and how many kilograms of sugar are needed to make 20 kg of sherbet? b) To make glass, 25 parts of sand, 9 parts of soda ash and 5 parts of lime are used. How many kilograms of glass will be produced if 250 kg of lime is used?

a) To find the cream needed:
- Total parts of sherbet = 16
- Parts of cream = 4
- Proportion of cream = \frac{4}{16} = \frac{1}{4}
- Cream needed for 20 kg sherbet = \frac{1}{4} \times 20 = 5 \text{ kg}

To find the sugar needed:
- Parts of sugar = 1
- Proportion of sugar = \frac{1}{16}
- Sugar needed for 20 kg sherbet = \frac{1}{16} \times 20 = 1.25 \text{ kg}

b) To find the total glass produced:
- Total parts of glass = 39
- Parts of lime used = 5
- Proportion of lime = \frac{5}{39}
- Total glass produced = \frac{39}{5} \times 250 = 1,950 \text{ kg}

Thus, the answers are:
a) Cream: 5 kg, Sugar: 1.25 kg
b) 1,950 kg of glass