Effect of 2x Commerce Event

It was bugging me that I couldn't exactly reproduce the amount of ducats obtained from selling under the current 2xCommerce event, so I did some experimenting. I think I've got it now. There's was an unexpected round-down to integer in an intermediate step in the working, expressed below as "floor".

When you sell, and a small window pops up showing ducats, experience, etc earned, note that the numbers in parenthesis for ducats have been included in the previous number. For example, if it reports ducats are "62520 (+3384)", then you obtained a total of 62520 ducats for the sale, and that includes 3384 bonus arising from commerce mastery bonus and perhaps use of a letter of guarantee.

The simple formula for proceeds of sale is

Quantity * unit buy price + event bonus * floor(quantity * unit base profit * (1 + master bonus + letter of guarantee bonus))

Example: Bought 22 items. Buy price = 2374. Sell price showing on trade window = 2531. So base profit per unit is 2531 - 2374 = 157. My commerce mastery bonus is 9%. Goblin letter of guarantee gives 40% bonus on trade goods. We currently have a 2 x commerce event. This gives the sales proceeds as

22 * 2374 + 2 * floor(22 * 157 * (1+9%+40%)) = 22 * 2374 + 2 * 5146 = 62520

An alternative equivalent formula is

Quantity * (unit buy price + event bonus * unit base profit) + event bonus * floor(quantity * unit base profit * (master bonus + letter of guarantee bonus))

For the example, this gives

22 * (2374 + 2 * 157) + 2 * floor(22 * 157 * (9%+40%)) = 22 * 2688 + 2 * 1692 = 59136 + 3384 = 62520

This form better matches the numbers reported in the window that pops up to report the results of the sale, which listed the ducats result as "62520 (+3384)"

When the event is over, we presumably just replace the 2 by 1 in the above. If not using a letter of guarantee, replace the 40% by zero. I've only tested with Goblin's letter of guarantee, and with no letter of guarantee. It would be good if someone with a different type of letter of guarantee could verify. It would also be good if it could be tested by someone with a different commerce master bonus.