Well, I do know that at least Soroban likes this kind!
Boat leaves point A, at constant speed b mph,
against a current of speed c mph for 1st hour.
The current's speed increases by 1 mph hourly.
Like, boat nets (1st 3 hours): b-c, b-(c+1), b-(c+2)....
At point B, after u hours, a hat falls out of
the boat, and floats with the current towards A,
and gets to A after travelling for v hours.
Boat continues for another w hours to point C,
where it turns around and heads towards A.
YES, the boat reaches A at same time as the hat!
Distance AB = d miles, distance BC = e miles.
Be advised that e - d = 39 miles.
Please note that w = 6 hours; you're welcome.
b, c, d, e, u, v, w are all integers.
Find b and v.