The number of molecules in one mole of any substance is equal to Avagadro's number
Avagadro's number is 6.023 X 10²³
Thus
1 mole = 6.023 X 10²³ molecules
for ammonia we are provided with three moles
so to obtain the total number of molecules of ammonia in three moles we will multiply the Avagadro's number with three
total molecules = 3 X 6.023 X 10²³
Total molecules of ammonia = 18.069 X 10²³
In scientific notation
Total molecules of ammonia = 1.8069 X 10²⁴ = 1.81 X 10²⁴