A natural gas contains CH_{4} 95 %, C_{2}H_{6} 3 %, CO_{2} 1 % and N_{2} 1 % by mole. Taking M = 16, 30, 44 and 28 kg/kmol and M_{air} = 28.97, find (a) the molecular mass of the gas (kg/kmol) and (b) its specific gravity.