Which number is prime? 36 37 35 38

A number is prime if its only divisors are 1 and the number itself.

Out of your numbers, 36 and 38 are even, and thus divisible by 2, so they aren't prime.

Similarly, 35 ends with 5, so it's divisible by 5, and is not prime.

37 is divisible only by 1 and 37, and thus it's prime.