Answer:
Explanation
first list all the factors of both of the terms
-63: 1,3,7,9,21,63,-1,-3,-7,-9,-21,-63
72: 1,2,3,4,6,8,9,12,18,24,36,72
Find the GCF
GCF=9
=-9(7x to the 5th power -8)
sorry it wont let me use powers
also side note, the GCF is negative because the leading term is a negative number. and its -8 because multiplying two negatives gives a positive.