It is little more than 5 miles between LaGuardia Airport and Harlem as a straight shot (in Manhattan).
If you are specifically asking for Midtown, it's between 6 and 6.5 miles (9.7 to 10.5 kilometers) from LaGuardia Airport to East 59th Street, JetBlack driving west on the Triboro Plaza, over the Robert F. Kennedy Bridge, and then down the East Side of Manhattan.