1. Find the amount of simple interest on $2,100 from September 2, 2010 to June 15, 2011 using the banker's rule.
2. Find the amount of interest on $3,000 at 7% for 50 days using both ordinary and exact interest.
3. Jennifer owes $600 due in 9 months and $1,500 plus 6% interest due in 3 months. She wants to pay off both debts in a single payment in 11 months. How much should she pay if the money is worth 5%?