I have a math question that I can't get

Question

A100ML pitcher of lemonade is currently 90% water and 10% lemon concentrate.How much water must you add to change the balance to 95% water a 5% lemon concentrate?

Answer 1

Since we are adding water we use the percentages of water.

w represents the amount of pure water

0.90(100) + x = 0.95(100 + x)

90 + x = 95 + 0.95x

0.05x = 5

x = 100