ANSWER
3:5
EXPLANATION
The given similar octagons have areas 9 m² and 25m² .
Let the scale factor of their side lengths be in the ratio:
m:n
![{( (m)/(n)) }^(2) = (9)/(25)](https://img.qammunity.org/2020/formulas/mathematics/high-school/1immu6sj4q3z5de5qfp7rvleamdzp7bxzx.png)
We take square root of both sides to get;
![(m)/(n) = \sqrt{ (9)/(25) }](https://img.qammunity.org/2020/formulas/mathematics/high-school/lo0up47getw82eenyysjwisrizyk82008j.png)
We simplify the square root to get
![(m)/(n) = (3)/(5)](https://img.qammunity.org/2020/formulas/mathematics/high-school/m0ec5471pusv8igh8eppp75bub1bghfvnl.png)
Therefore the scale factor of their side lengths is 3:5