To give a 18kg child a ride, two teenagers pull on a 3.3 kg sled with ropes, Both teenagers pull with a force of 55 N at an angle of 35 degrees relative to the forward direction, which is the direction of motion. In addition, the snow exerts a retarding force on the sled that points opposite to the direction of motion, and has a magnitude of 57 N. What is the acceleration of the child and sled?