CH4
If the compound has 25% hydrogen and 75% carbon, assume there is a 100 g sample composed of 25 g of hydrogen and 75 g of carbon. Use the molar mass of each element to convert the gram amounts to moles and you have 25 moles of hydrogen and 6.25 moles of carbon. Divide each by 6.25 and you have 4 moles of hydrogen for 1 mole of carbon and an empirical formula of CH4
