A recipe uses 5/8kg of flour to make 10 cakes.

How much is needed to make 30 cakes?

10 cakes required 5/8 kg of flour.

1 cake would require (5/8) / 10 = 5/8 * 1/10 = 1/16 kg of flour

30 cakes would then require = 30 * 1/16 = 30/16 = 15/8 kg

30 cakes would require 15/8 kg of flour.