In this question, it is given that
Harish tthought of a two digit odd number greater than 50. One of its digits was half the other.
Since it is a two digit odd number. So for the number on one's place, we have 5 options which are 1,3,5,7,9. And none of these can be double .
And in the ten's place, it have to be greater then 5. So we have two options, 6 and 8.
And double of 3 is 6, so the number is 63.