Yes , reducing in simplest terms is very important regarding fractions which still have a chance to get reduced.
how do we reduce?
We commonly/usually reduce them with their suitable factors or in which table they go (multiplication factors)
So as 2/4 is reduced into 1/2 , here 2 and 4 are multiples of 2 and can be reduced into their simple forms as 1 and2
Because 2 x 1 = 2 and 2 x 2 = 4
So now considering the question. , 9/45
This can be reduced in two ways
With factors of three first!
=> 9/45
This goes in three table as 3 x 3 = 9 and 3 x 15 = 45
So we get it as 3/15
And we can again simplify this with 3
3 x 1 = 3 and 3 x 5 = 15
Which comes out to be 1/5
Now second method ;
Directly with 9 table
We know , 9 x 1 = 9 and 9 x 5 = 45
Can be reduced as 1/5 easily.
Also refer attachment