An alloy contains copper and zinc in the ratio 7 : 3. If it contains 12.6 g of copper, how much does this alloy weigh?

Reena weighed 63 kg. She reduced her weight in the ratio 9 : 8. Find her new weight.

Two numbers are in the ratio 5 : 8 and their difference is 12. Find the numbers.

If a : b = 3 : 2 and b : c = 4 : 5, find a : c.