Marty was paying off a television that he bought on layaway, which means he has to pay it off over a period of time. Marty made 3 upfront payments over three weeks. One week he paid $20, next week $30, and the next week $40( remember he paid some money already). The total cost of the tv was $690. He will now make monthly payments to pay off the rest that he owes. If he has another 12 months to pay it off, how much will he have to pay per month?