Well, there are #20*mol# of hydrogen, so approx. #20*g#........
Explanation:
In one mole of methane we have a mass #16.0*g#. Carbon constitutes #12*g# of this mass, and #4*g# of this are hydrogen. If there is a #5.0*mol# quantity of methane, clearly there are #4xx5*mol# hydrogen, and a mass with respect to hydrogen of approx. #20*g#. What is the mass of carbon in this quantity?