First of all factor both of the numbers.
405=5*3^4
450=5^2*3^2*2
Now line it up.
5*3*3*3*3
---------------
5*5*3*3*2
Now we can cancel out some numbers and get
3*3
-----
5*5
Now we actually multiplies them again and get.
9/10
This is the process of how to get it hope it helped!
