Infinity is not usually considered as a number.

One can get very pedantic about this — if we want to fully specify the problem we need to define what number system X is a part of (reals, integers, natural numbers, etc) None of those number systems I named include infinity, so infinity can’t be a solution under those definitions of the problem.

But if we say X is an element of the super-reals (real + infinity) then infinity can be a solution