the answer would be:
(13/52 * 39/51 * 38/50 * 37/49) + (39/52 * 13/51 * 38/50 * 37*49) + (39/52 * 38/51 * 13/50 * 37/49) + (39/52 * 38/51 * 37/50 * 13/49)