The closure property of subtraction of two numbers a and b is possible only if​

a, b and a - b all come from the same set

Step-by-step explanation:

"Closure" for an operation means that the two numbers and the answer after the operation is done all come from the same set of numbers.

Example:  The set of positive integers (counting numbers) is closed under addition -- (positive integer) + (positive integer) = (positive integer)

But the set of positive integers is not closed under subtraction --  8 - 10 = (not a positive integer)