An airplane is sent on a rescue mission to help a stranded explorer near the South Pole. The plane cannot land, but instead drops a supply package of mass m = 58 kg while it is flying horizontally with a speed of vp = 116 m/s. The supply package drops onto a waiting sled that is initially at rest. After the package lands in the sled, the speed of the sled plus package is found to be 38 m/s. What is the mass of the sled?