What is the percent by mass (%m/m) concentration of ammonium hydroxide (nh4oh) in a solution prepared by dissolving 8.40 g nh4oh in 94.60 g of h2o?

If you want to express the concentration in terms of percent mass, then you would have to divide the mass of solute to the mass of solution, then multiply it by 100.

Mass of solute = 8.40 g

Mass of solution = 8.40+94.60 = 103 g

Percent Mass = (8.40/103) * 100 = 8.16%