# Where am I making a mistake in my calculation of profit on a short-sale?

I am studying financial math and here is a problem and the solution from the author:

Here are my calculations:

The short sale is $200\cdot24.82 = 4964$. Now half of this amount will be taken for a haircut and $0.3$% will be taken for a commission. Then we will have (0.5)(0.997)4964 = 2474.55 at t = 0. At t = 3 months, we will have $2474.55e^{0.06 \cdot 0.25} = 2511.95.$

Covering the short position at t = 3 requires 200(21.64) = 4328. The close commission is 200(21.64)(0.003) = 12.98.

We will receive the haircut and rebate which will be $4964(0.50)e^{0.04 \cdot 0.25} = 2506.94.$

The profit is then 2511.95 - 4328 - 12.98 + 2506.94 = 677.91.

$$2474.55*e^{.06/4}-2474.55e^{.04/4} = 12.53$$