What do they stand for?

What are the resulting coefficients when you balance the chemical equation for the combustion of ethane, c2h6? in this reaction, ethane is burned in the presence of oxygen (o2) to form carbon dioxide (co2) and water (h2o). (g)+(g)→(g)+(g)

Fill in the coefficients that will balance the following reaction: a0cr2(so4)3 + a1agno3 -> a2cr(no3)3 + a3ag2so4

What is the percentage composition of carbon in the compound ch4