Is prime factor of `A` is 3 and prime factor of `A` is 7 then find the prime factor of A+B.Show with proper working

If two numbers have 3 and 7 as their lowest factor then this number should be odd number because if there even their least prime factor must be 2. So A and B are odd numbersWe know that sum of two odd number is an even number.Therefore A + B is an even number and smallest prime factor of an even number is 2.So our required answer is 2.