To calculate the GCF, you need to list all the prime numbers that will go into each number listed
12: 2, 2, 3
60: 2, 2, 3 5
68: 2,2,17
Now you circle the numbers that are the same in each.
GCF: 2, 2
Multiply these numbers to find the GCF: 4
Answer:C B A
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Khan academy has a lot on this sorry I couldn't answer bro
If they get unexpected results they could note what they could've done wrong or what they could change in a next trail of experiments. Or look back and see what different happened to they could've hypothesized. There could be many different courses on what to do next.