How many moles of carbon atoms are equivalent to 38.1 g carbon?
Your tool of choice here will be the molar mass of carbon, which you can use as a conversion factor to figure out how many moles of carbon would be present in that sample.
You can use the molar mass of carbon as a conversion factor because it represents the mass of
#color(blue)(ul(color(black)("molar mass C " = " mass of 1 mole of C")))#
Now, carbon has a molar mass of
This means that your sample will contain
#38.1 color(red)(cancel(color(black)("g"))) * "1 mole C"/(12.011color(red)(cancel(color(black)("g")))) = color(darkgreen)(ul(color(black)("3.17 moles C")))#
The answer is rounded to three sig figs, the number of sig figs you have for the mass of the sample.