Here's my confusion:

Assume your average credit sales are $50 million per year and average accounts receivable are $5 million. A factoring company offers you an agreement that it will be buying your accounts receivable at a 2.20% discount. Your bank offers you a credit at R% per year (actual yearly rate). 

What would be the minimum R% for which you would choose factoring? That is, what is the rate R% offered by the bank at or below which you would rather borrow money from the bank instead of factoring?

If the AR was purchased at a 2.2% discount, that means that the company would receive $4,890,000, right? I'm not even sure how that helps me get to an answer- am I trying to figure out the interest rate offered to earn the full amount of the AR?