For a two-digit number, the sum of the number in the ones place and the number in the tens place is exactly 9, and the number in the tens place is 8 times the number in the ones place. What is the two-digit number?
一个两位数，个位上的数和十位上的数之和正好是9，十位上的数是个位上的数的8倍，这个两位数是多少．
<result>81</result>