A number here means any real number.
It's still infinity. "Infinity" isn't really a single number. It's a shorthand expression for the limiting
case of a number that is bigger than any number you can name. Mathematicians (except in very
informal discussions) never speak of "this number equals infinity." They say "this number approaches infinity," meaniung "let's look at what happens when this number gets bigger than any number we can possibly think of."
So when you speak of "infinity divided by a real number" you are still talking of a number that's bigger than any number you could name. If that still doesn't make sense, just think "Okay, you want to divide infinity by a number N. Well, I'll take he biggest number I could think of before you came along and multiply it by N and my infinity is bigger than THAT number."
infinity divided by 4?
∞/x = 1/(0*x) = 1/0 = undefined → ∞
it will be always infinity....