It's a snowy day and you're pulling a friend along a level road on a sled. You've both been taking physics, so she asks what you think the coefficient of friction between the sled and the snow is. You've been walking at a steady , and the rope pulls up on the sled at a 21.0 angle. You estimate that the mass of the sled, with your friend on it, is 64.0 and that you're pulling with a force of 84.0.