问题
问答题
Laura borrowed $240, interest free, from her parents to pay for her college education. If she pays back 
percent of this amount quarterly, and has already paid $42.00, for how many months has she been paying back her loan ？
答案
参考答案：
21个月
解析：
Laura每季度偿还的钱为[*]美元，她还了42美元，所以她已经还了42÷6=7个季度，也就是21个月。