To calculate cannibalization:

The case says that it will be between 10-20% cannibalization. That means each different retailer they currently have will lose that amount of sales if the company sells online. Use 15% to make it easy.

Other important numbers.

860,000 total sold

$30.64.average price per pair.

I believe, there is data in the case about what percentage of total sales goes through certain types of retailers. The total is given on Blackboard, the average price, and the % of cannibalization.

Total units x avg price = total sales volume in dollar terms

Cannibalization total = 15% x total sales volume

The major partner stores have some % and then all the small retailers have the rest.

Major partner stores % x cannibalized total = amount major partners lose

Small retailer stores % x cannibalized total = amount small retailers lose.

Small retailer loss + major partner stores loss = total cannibalized

Who is the biggest loser? Who can actually continue in business with that loss?