First find common factor for parameters. I mean to find common factor number 9,15,12 first, write the divisors: Divisors of 9: 1,3,9 divisors of 12: 1,2,3,4,6,12 divisors of 15: 1,2,3,5,15 so see, that GCF of 9,12,15 is 3.
Now, count GCF of x^2, x^4, x^6 GCF 2,4,6 is 2, so the result is x^2 and know finally GCF these terms is
The researchers used data from 10 trials so they could compare each trial or use the information in all, its better to use more than one so you can compare and see the difference.