Question on probability

Carson Products sells sweatshirts and is preparing for a World Cup Soccer match. The cost per sweatshirt varies with the quantity purchased as follows:

Quantity                      Unit cost

4000                            $14

5000                            $13.5   

6000                            $13 

7000                            $12.5 

   Carson must purchase the shirts one month before the game and has analyzed

   the market and estimated sales levels as follows.

Unit sales              4000           5000           6000           7000

Probability               15%           20%             35%              30%

               
The estimated selling price is $25 for sales made before and at the game day. 

 Any shirts remaining after game day can be sold at wholesale to a local 

 discount store for $10.

 The expected profit if Carson purchased 6,000 shirts is :

• $69,000.
• $72,000.
• $64,500.
• $66,000.

 I am not able to arrive at correct answer which is $64,500.  I request anyone to please help.

Thanks