This question is mainly to find out what the elements of the two sets are.

The element of a set is x, and the element of b set is 9/( 10-x), and they are all natural numbers.

Because when x= 1, 9/( 10-x)=9,

When x = 6,9/(10-x) = 3,

When x=9, 9/( 10-x)= 1,

So a = {1, 6,9} and b = {9 9,3, 1}

The intersection of a and b = {1, 9}.