standard form

[hot gulch]

my poopoo yr10 brain cant compute this

[pallid eagle]

lets call the mass of the hydrogen atom h and the mass of the carbon atom c. you would do 4h+1c in your calculator and round to 3 sig figs for part a because there are 4 hydrogen atoms and 1 carbon atom. lets call this answer m (for methane). for part b, all you do is 1/m in your calculator and round to 3 sig figs because it's (number of molecules) = (total mass)/(mass per molecule)

[hot gulch]

<3