Ok
so the math that we need to do for this problem will be:
Total number of families = 240
minus the ones that don't have any pets = 91
minus the families that do have dogs = 91
minus the families that do have cats = 70
add back the overlap of dogs and cats = 31
add back the overlap of dogs cats parakeets = 7
240 - 91 - 91 - 70 + 31 + 7
^ this math will give us the families that ONLY have parakeets
so I stand by what I said before that this is the math you would to do get the answer to your problem
therefore its 26 buddy