The greatest common factor is... 5a I got this by... 10: 1,2,5,10 15: 1,3,5,15 25: 1,5,25 The GCF is 5 for the numbers. For the a's, it's... a: a a^3: a×a×a a^6: a×a×a×a×a×a The GFC is a. Then multiple 5 and a, and you get... 5a The GFC is... 5a Hope this helps!