Explanation

Step 1: Find the prime factors of each number

255 = 3 × 5 × 17

345 = 3 × 5 × 23

495 = 3² × 5 × 11

Step 2: Identify the common factors

The common prime factors are 3 and 5.

Step 3: Calculate the HCF

HCF = 3 × 5 = 15