We have to note that π is an irrational number. It cannot be written as a fraction of two integers; 22/7 is merely just an approximation of π, not π itself.
π - 22/7 involves subtracting a rational number, 22/7, from an irrational number, π. Since subtracting a rational number from an irrational number results in an irrational difference, π - 22/7 is irrational.
