[填空题]
A 95-kg halfback moving at 4.1m/s on an apk5m n/8 akl5kppare6 t5imd/ (pz7or)adx 8/ uaokgnt breakaway for a touchdown is tackled from behind. When he was tackled by an 85-kg cornerback running at 5.5m/s ixz/pg765)aauord/ o kt d im8(n the same direction, what was their mutual speed immediately after the tackle? m/s
