Mark Harris, 21, a George Washington University political science major who is just preparing to graduate, scored a stunning upset over longtime Republican incumbent Rep. Tom Stevenson, R-Mt. Lebanon. Mr. Stevenson, 53, voted in favor of the legislative pay raise, accepted the money, then returned it. Late in the campaign, his supporters ran TV spots calling attention to Mr. Harris’ lack of political and life experience. Mr. Harris responded by sending Mr. Stevenson a copy of the book “Economics For Dummies.” Daniel Hackett, 49, of Mt. Lebanon ran third in the GOP contest.