1. The problem statement, all variables and given/known data A worker applies a force of 210N to a box attached to a cart, with sufficient frictional force such that the box and the cart move as one. What is the frictional force on the box? Force 1: Force on box by worker, FBW Force 2: Force on cart by box, FCB Force 3: Force on box by cart, FBC 2. Relevant equations 3. The attempt at a solution This is from the solution, but I can't understand how it was obtained, as it doesn't explain the process: FCB = McartA (I knew this part) FBW - FBC = MboxA "Since we want to solve for the unknown FCB = FBC, we eliminate A from these two equations and obtain:" FCB = (Mcart*FBW)/(Mcart+Mbox) I don't quite understand what they mean by "eliminate A" (hold it constant?), nor can I seem to deduce the process they used here. I've tried substituting in McartA for FBC (since they're equal), but all that does is solve for A, which I'm evidently supposed to eliminate to begin with.