Yes it can be simplified because 21 and 108 are multiples of 3.
Use the divisibility by 3 rule to add the digits to check.
- 2+1 = 3 which is a multiple of 3
- 1+0+8 = 9 which is a multiple of 3
Let's divide 21 and 108 by 3 to reduce.
The fraction 21/108 reduces to 7/36
We cannot reduce further because 7 and 36 do not have any factors in common other than 1.