Answer:
1) 3
2) 30
Explanation:
To find the GCF, you find out the (prime) factors of the two numbers in question. For this question, we would find the (prime) factors that go into 6 and 15.
For the number 6, we can get 2 x 3 = 6.
For the number 15, we can get 3 x 5 = 15.
You then underline those factors that you have in common. As you can see, since there is only 1 factor underlined per number, we would have the GCF as 3. On the instance you have more than 1 number underlined, you just multiply them.
Example: 12 and 20
2 x 2 x 3 = 12
2 x 2 x 5 = 20
They both have 2 x 2 in common, so you would get 4 as the GCF.
Moving onto the LCM, I would find this by multiplying each number until i find something similar.
6 x 1 = 6
6 x 2 = 12
6 x 3 = 18
6 x 4 = 24
6 x 5 = 30
15 x 1 = 15
15 x 2 = 30
The number that is underlined is the lowest common number we have when multiplying and going up by 1, so 30 would be our answer.
A faster way you could've solved this is by knowing that you can't multiply 6 and a whole number to get 15, but you can multiply 6 and a whole number to get 30. This, however, is just prior knowledge.