Dont bother with Spot On l, much cheaper to buy Ivemectin and simply apply a few drops on the back of the cats neck. It will also deal with most intestinal worms as well (except tapeworm)
I got a farmers pack, brand name Ivomec, 200ml about three years ago.
Have only used half on my menagerie of dogs, cat and bird. For the $140 it works out to be ridiculously cost effective.
I reckon if you talk nicely to your local Bovine vet, they may sell you $50 bucks worth and that should do your two for the next ten years or so..

As for the computer, hit the friggin thing with a hammer already!