When Xiao Ming multiplied the two-digit number by 4, he exchanged the digits in the ones digit and the digits in the tens digit of the two-digit digit, and the calculated product was 84. What should be the two digit number.
小明在计算两位数乘4时，将两位数个位上的数字与十位上的数字交换了位置，结果算出的积是84．这个两位数字应该是多少．
<result>12</result>