Whip out the instamatics everyone. Believe it or not it's been four years since The Facts of Life NBC's sitcom set in a girls school -- begin its run. Now in an episode scheduled for May 4 the first class of regular characters graduates. Stuck-up Blair (Lisa Whelchel, left) and tomboy Jo (Nancy McKeon) will leave Eastland School and enter the fictional Langley College. But don't despair, fans, relatives and agents. Blair and Jo will be an integral part of next seasons Facts as well newly minted high-school seniors Tootie (Kim Fields) and Natalie (Mindy Cohn)