IMU has three components: operating expenses, anticipated markdowns and desired profit. Operating expenses -- utilities, payroll, supplies, insurance and other costs such as marketing and shrinkage, or loss from theft or damage -- make up your overhead and are expressed as a percent of sales.
See the following table for the approximate number of crabs per bushel: Generally speaking, a bushel of Number Ones will hold 60 - 70 crabs depending on how big the crabs are at that time of year. If there are 60 - 70 crabs, they will feed about 10 - 12 people depending upon what else is on the menu.
The price per bushel quoted on the CME is in cents per bushel, so $8 per bushel. The contract size is 5000 bushels. Contracts are the units that you trade on the CME. So in order to buy one contract you would need to have $40k.