On first blush, we might consider the answer to be "0.'
But, it's not.....
Consider the set of integers on the number line. You will agree - I hope - that this set is infinite. Now, consider the set of even integers on the number line. Again, we'll consider this set to be infinite, too.
So, subtracting the second "infinity" from the first "infinity," we end up with another infinite set - the set of all odd integers !!
Thus, ∞ - ∞ = ∞
Also, notice another odd property......I've divided one set in half and gotten another infinite set. Thus....
∞ / 2 = ∞
One more interesting idea, and then I'll shut up. Which "infinity" is "greater?" The set of all positive integers, or the set of all positive even integers??
Note, that I can "count" each positive even integer.....For example, 2 is the first one, 4 is the second one, etc. Thus, I can put each positive even integer into a one-to-one correspondence with a "counting" number. And since I can do so, then the set of positive even integers must be just as large as the set of all the positive integers !!!