Hey there!
25: 1, 5, & 25
because: 5 * 5 = 25 & 1 * 25 = 25
45: 1, 3, 5, 9, 15, 45
because: 1 * 45 = 45, 3 * 15 = 45, & 5 * 9 = 45
Common factors: 1 & 5
The bigger number of those two is 5
Therefore, your possible answer is: 5
Good luck on your assignment and enjoy your day!
~Amphitrite1040:)