You know that if acid gets on the skin, the affected area is washed with water and then treated with

You know that if acid gets on the skin, the affected area is washed with water and then treated with a 3% sodium bicarbonate solution (baking soda). A solution weighing 150 g with the indicated mass fraction of soda was evaporated to 110 g. Calculate the mass fraction in% of soda in one stripped off solution.

Calculate m (soda) in solution before evaporation:
m (soda) = m (solution) * w (soda) / 100 = 150 * 3/100 = 4.5 g.
Calculate w (soda) in solution before evaporation:
w (soda) = m (soda) * 100 / m (solution) = 4.5 * 100/110 = 4.1%