Hi, There is something weird here: Please look at problem and solution. When I set my equations: 2000a=2000gsin(30°)-T 1800a=-1800gsin(20°)+T I add them up: 3800a=2000gsin(30°)-1800gsin(20°) a=1m/s^2 Now I want to equilibriate the car: The force of brakes=-2000a=-2000a=-2000N. But the book has a different answer. I understand their method. But why is my method wrong? Please try to explain to me in detail clearly. I have difficulty understanding.