When Xiaohong calculated 6.3 divided by a number, because the decimal point of the quotient was wrong by one place to the right, the result was 15. What is the divisor of this question?
小红在计算6.3除以一个数时，由于商的小数点向右点错了一位，结果是15，这道题的除数是多少？
<result>4.2</result>