If the two digits of the age of Mr. Manoj are reversed then the new age so obtained is age of his wife. 1/11of the sum of their ages is equal to the difference between their ages. If Mr. Manoj is elder than his wife then find the differences between their ages. Ans: 9 years how?

Found this nice group on FB. Posting a question from the group here:
If x and y are positive real numbers such that 12xy + 21x + 20y = 46, find the minimum value of 3x + 4y.
1\. 6 2\. 7 3\. 8 4\. 9
Source: https://www.facebook.com/groups/crackingcat