Question

Calculate the molecular weights for NH3 and SF6.

Answer 1

do you have a periodic table handy?

Answer 2

ok. you're going to need it for the masses of the elements.
\(NH_3\) has 1 nitrogen atom and 3 hydrogen atoms. From the table, the mass of nitrogen is 14.007 g/mol and the mass of hydrogen is 1.008
So the molecular weight is
\(14.007 + 3(1.008)=17.031~g/mol\)