The first thing you want to do is list numbers that add up to 10. When you get these numbers, ask yourself, "is 12 a multiple of both of these numbers?"
So, list your number pairs that add up to 10.
10 + 0 = 10.
12 is NOT a multiple of both numbers.
9 + 1 = 10.
12 is NOT a multiple of both numbers.
8 + 2 = 10
12 is NOT a multiple of both numbers.
7 + 3 = 10
12 is NOT a multiple of both numbers.
6 + 4 = 10
12 IS a multiple of both numbers.
5 + 5 = 10
12 is NOT a multiple of both numbers.
The number pair that adds up to 10 and has 12 as a multiple is 6 and 4. Now we have to find out if 12 is the LEAST common multiple of these numbers. List the multiples of both numbers until you get a common multiple for both of them. If that common multiple is 12, then the answer is correct.
6: 6, 12.
4: 4, 8, 12.
12 is, in fact, the least common multiple of 6 and 4, and the sum does add up to 10. The numbers 6 and 4 are your correct answer.