Common factors of 72 and 45?

The factors of 45 are: 1, 3, 5, 9, 15, 45

The factors of 72 are: 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72

The common factors are: 1, 3, 9
everyone knows that you have to find the factors of 45 and then 72 and then find what they have in commen and then find the highest now work it out ya self