If Marie and Calvin dissolve 50 grams of KBr in 100 grams of water at 90oC, the solution is

The solution is 50 %wt

Explanation:

50% wt is a sort of concentration and means, that 50 g of solute (in this case, the potassium bromide) dissolved in 100 g of water.

It is the same to say, that there are 50g of KBr for every 100g of H₂O