Answer:
23
Explanation:
To find the Greatest Common Factor, or GCF, we need to factor the first 2 numbers and then find the greatest number that is both present in the prime factorization of both numbers.
253 = 1 * 11 * 23
345 = 3 * 5 * 23
Since 23 is both present in both numbers and is the greatest, the GCF of 253 and 345 is 23.