Answer:
20/81
Step-by-step explanation:
Without parentheses, it is hard to tell what you are dividing. We assume you want ...
(4/9)/(9/5)
Then ...

_____
As written (without parentheses), your expression is evaluated left to right, so evaluates to ...
4/(9·9·5) = 4/405
It helps to imagine the variable a sort of as a unit. Like with 5 minus 12 lemons, it has no bearings on the addition/subtraction here.
Factor out a and subtract.
composite numbers less than 12={1,3,4,6,8,9,10}