To find the common factors of two numbers, just go through numbers in your mind from least to greatest and divide them into both numbers to see if they work. You can use a calculator for your division, if you'd like.
45 - 1, 3, 5, 9, 15, 45
63 - 1, 3, 7, 9, 63
The common factors of 45 and 63, other than 1, are 3 and 9.
Hope this helps!
