which of the following numbers are prime numbers 39 , 87 , 51, 31?​
prime numbers
31
Remember that
Prime numbers are numbers that have only 2 factors: 1 and themselves
51 is not a prime number
because
is a composite number and can be factored by any of the following numbers: 1, 3, 17, 51
39 is not a prime number because can be evenly divided by 1, 3, 13 and 39
87 is not a prime number because 3 and 29 as the prime factors of 87
therefore
answer is
31