In the formula, ch4, the percent composition of all elements is:
a. 75% c, 25% h
b. 25% c, 75% h
c. 81% c, 19% h
d. 20% c, 80% h

The problem is not clear if the percent composition is in terms of mole or mass. I will just present the two.

For mole percent.

Total number of moles of element per mole CH4 = 1 mol C + 4 mol H = 5 mol

therefore we have
% mol C = 20%
% mol H = 80%

for mass percent'

Molar mass of CH4 = 16 g/mol
 molar mass of C = 12
molar mass of H = 4*1 =4

thus
% mass C = 12/16 = 75%
% mass H = 4/16 = 25%

both answers are in the choices but percent composition is usually expressed in mass therefore I think choice A would be the best answer. 

Yesbyes h2yhh8 id thr answer to your wuestiob

Do u have the n? or maybe the m?