Mass percent of ammonia=18.6%
So, 18.6=(Mass of ammonia/mass of solution) *100
18.6=(mass of ammonia/volume of soln*density)*100
Mass of ammonia/volumeof soln=18.6*density*100=18.6*0.93*100=0.173g/ml.
The mass of NH3 is 0.173g/ml.
Hope you.
Dont need to realize, only use siple formula.