Given that "The animal caretakers can clean 8 outdoor cages in the same amount of time it takes to clean 12 indoor cages. "
It is obvious that if number of cages increase then time to clean them will also increase.
That means ratio of time for cleaning outer to indoor cage will remain fixed.
So we can setup proportion to find the time to clean up outer cage.
Let number of outdoor cages that can be cleaned in same time that is taken for 81 indoor cages = x
Then proportion can be written as:



x=54
Hence final answer is 54.