A father wanted to show his son what it might be like to borrow money from a financial institution. When his son asked if he could borrow $120, the father lent him the money and set up the following arrangements. He charged his son $6 for the loan of $120. The son therefore received $114 and agreed to pay his father 12 installments of $10 a month, beginning one month from today, until the loan was repaid. Find the approximate rate of simple interest the father charged on this loan.