Answer:
43
Explanation:
All the even numbers have a factor of 2, so we can eliminate 56 and 34. 75 ends in a 5, so that cannot be a prime number (ending in 5 is a multiple of 5). The sum of the digits of 63 (6+3) is 9, and that is divisible by 3, so that number is also not prime. 43 is a prime number.