Mary is planning to buy a mobile phone that costs $500. A salesperson at the store informs her about four different installment plans that she can choose from. plan A: a down payment of $50 and monthly payments of $40 for 12 months
plan B: a down payment of $100 and monthly payments of $80 for 6 months
plan C: no down payment and monthly payments of $60 for 12 months
plan D: no down payment and monthly payments of $100 for 6 months

Which plan will have the highest finance charge?