That will depend on the plus or minus values of 6 and 38 which have not been given.
It is 38.
23 28 33 38 43 48 53 (+5...)
6.37704216
53 58 63 68
(71/6) - (61/3)= (43/6) - (19/3)= (43/6) - (38/6). . . =5/6
33/38 = 33 ÷ 38 ≈ 0.868
43 - 5 = 38
0.7674
33
33 + 38 = 71
43 is a prime 33 is composite
The GCF is 1.