Mixture problem

Question

a chemist has 30g of a 10% salt solution. He wants to increase the salt content to 20% . How much water does he need to evaporate?

Answer 1

30 g of 10% salt soln = 3 g salt + 27 g water

In order to have 20% salt from those 3 g of salt, you need a total mass of 15 g or 3 g salt + 12 g water. So you need to evaporate 15g of water and assuming a density of 1g/ml y would evaporate 15 ml.