Number of molecules = number of moles x avogadros number
So given the above equation, we have to start by calculating NH3 number of moles.
n = m/M where m is the mass (367.2 g) of NH3 and M is the molar mass (17.031 g/mol)
n = 367.2/17.031
n = 21.56 mol
Avogadros number = 6.022x10^23 mol-1
number of molecules = 21.56 mol x 6.022x10^23 mol-1
number of molecules = 1.299x10^25