Solve Calculate the grams of carbon of 77.7 g of propane?

Answer 1

Use proportions:
Mass of carbon
=77.7g *(sum of RAM of carbon atoms in propane)/(Mr of propane)

RAM=relative atomic mass
Mr = relative molecular mass

Answer 2

C3H8 = propane.
%C = (3*atomic mass C)/molar mass C3H8.

Then g C = %C (as a fraction) x 77.7.