Oh man i hate these questions its giving me headaches can any body help me out?

Question

How do you calculate the relative formula massof SnF2

Relative atomic masses: F=19 ;Sn=119

And how do you calculate the percentage by mass of fluorine in SnF2

Answer 1

The atomic mass of SnF2 is the atomic mass of Sn plus double the atomic mass of F. (19*2) + 119 = 157

100% = 157

x%    =  38

x = (38*100) / 157 = 24.203821656050955414012738853503 %