Blast furnace gas in a steel mill is available at 500 F to be burned for the

Question:

Blast furnace gas in a steel mill is available at 500 F to be burned for the generation of steam. The composition of this gas is, on a volumetric basis,
Component CH4 H2 CO CO2 N2 H2O
Percent by volume 0.1 2.4 23.3 14.4 56.4 3.4
Find the lower heating value (Btu/ft3) of this gas at 500 F and P0. Of the six components in the gas mixture, only the first 3 contribute to the heating value. These are, per lb mol of mixture: