Thanks, But according to your illustration, B should be 7u +2u = 9u. How did it become 5u in the 2nd row?
And how did reducing 40 cards becoming 1u less for B?

Blimey, you’re right. Thanks for pointing that out!

As for how I obtained 4u for B in the end, it is because the total units for all 3 people at the end have to be 14u (internal transfer). Since we know A had 2u and C had 8u, B had 4u after.

Thanks!