What masses of kbr and water are needed to produce 300. g of a solution that is 3.00 % by mass?

In a solution of KBr and water; KBr is the solute and water is the solvent;

Therefore; to achieve 3% by mass; it means we are going to have 3% of the mass being the solute and the other 97 % being the solvent.

Thus; KBr (solute) = 3/100 * 300 (total mass) = 9 g

Hence; the appropriate masses will be; 9.00 g of KBr and 291 g of water.