There is a two-digit number. The ratio of the ones digit to the tens digit is 3:1. If the tens digit is added with 6, it will be equal to the ones digit. What is the two digit digit?
有一个两位数，个位上的数与十位上的数的比是3：1，如果十位上的数加6，就和个位上的数相等，求这个两位数是多少？
<result>39</result>