Integers are the numbers that are positive or negative like -3, -2, -1, 1, 2, 3
Natural numbers are the numbers that we use to count like 1, 2, 3, ...
Rational numbers are numbers that can be written as a/b like 2/3, 1/5
Irrational numbers are decimal numbers with no sequences.
So, the day d for which an appointment is scheduled is a natural number because is a number between 1 and 31.
Answer: natural numbers
