From Fallen London Wiki (Staging)

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Right you are. That is...

(60 + 2.5 × 5.5 + 22.5 × 2.5 - 6 × 12.5) / 8A = 6.875 EpA (if sold individually)

or

(60 + 2.5 × 5.5 + (2.5 + 85/5) × 2.5 - 6 × 12.5) / 7.2A = 6.59 EpA (if sold in bulk)