Okay, so to start you need to find the molar mass for one molecule of CH4.
C=12.0g
H4=4.00g
So, CH4 molecular mass (or one mole of CH4) is 16 grams. You can then just divide 10.3 grams by 16 grams, which gives you an answer of .644 moles of CH4. Hope this helps!
