75) how many molecules of ch4 are in 48.2 g of this compound?

The molar mass of CH4 is 16.0 g/mol.  

48.2 g CH4 x (1 mol / 16.0 g) = 3.01 mol CH4  

1 mol = 6.02 x 10^23 molecules  

3.01 mol CH4 x (6.02 x 10^23 molecules / 1 mol ) = 1.81 x 10^24 molecules