How many grams of nh3 are needed to provide the same number of molecules as in 0.15 grams of sf6

Moles of SF6 = 0.15/molar mass of SF6 = 0.15/146.06 = 1.02 x 10⁻³ moles.
Moles of NH3 = Moles of SF6 = 1.02 x 10⁻³ moles.

Therefore mass of NH3 = moles of NH3 x molar mass of NH3 
                                       = 1.02 x 10⁻³ x 17.03
                                       = 0.017 grams.