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Porthos is one of the Three Musketeers!
Explanation
You may remember from a few weeks ago that whilst domestic gas and electricity is subject to the lower rate of 5% VAT, other supplies of gas and electricity (generally commercial supplies, including to office buildings) are subject to the standard rate of 20%.
(4x4x4) - (2x2x2) = 64 - 8 = 56