12 yuan, let 36,

Rent X (X must be less than or equal to 36), and the rent price is: (36-X)/2 X(50%)+ 12.

Explanation: 36-X is a ship that has not been rented out because of the price increase.

(36-X) /2 is a multiple of 2 for ships that are not rented out.

If two boats are not under-rented, and the rent is increased by 50%, then the rent is increased by (36-X)/2x50% for each boat under-rented.

The increased price plus the original amount is the rental price: (36-X)/2 X 50%+12.

Simplified as: 2 1-X/4

Then the profit is equal to: rental quantity x price = X * (2 1-X/4).

= - 1/4*X^2 + 2 1X

Formula:-1/4 (X-42) 2+42 2

It can be concluded that X.

Then: rent 42, the biggest profit.

But at most, only 36, 36 is less than 42, which belongs to the monotonic increasing interval, so renting 36 is the most profitable.