You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: HOW DO THEY WORK? 
Clue: Many car salesman work on "straight" this, though you're better off buying from one who's on salary
commission

Category: THE COMPUTER AGE 
Clue: Dan Bricklin developed VISICALC, the first of these programs, similar to an accounting ledger
spreadsheet

Category: BEGINS & ENDS IN "K" 
Clue: Mark Twain once worked as a printer in this Iowa town

keokuk