How many moles of (nh4)2s are there in 150 g of (nh4)2s?

The answer
the number of moles can be found easily by using formula of molar mass

Molar mass = mass (g)  / number of moles (mol)

from this, we can get number of
 
number of moles (mol) =mass (g)  / Molar mass

the mass molar of (NH4)2S :
M((NH4)2S) = (14+ 4x1) x 2  + 32 = 36+32 = 48 g/ mol

number of moles (mol) = 150 g / 48 = 3.12 moles