In 2003, the US consumed (a) 20 MMbd of crude oil. (b) 21.9 tcf (trillion cubic feet)

Question:

In 2003, the US consumed
(a) 20 MMbd of crude oil.
(b) 21.9 tcf (trillion cubic feet) of natural gas.
(c) 1 billion tons (short) of coal. The Btu equivalents are as follows: 1 bbl crude oil: 5.8 million Btu; 1 Mcf gas: 1.03 million Btu; 1 ton coal: 21 million Btu. Compare the energy consumption in the consistent unit of Quad (1 Quad = 1015 Btu).