The problem is attached. I am supremely stumped. First and foremost, what the heck does "horizontal forces" mean? If they are both horizontal, how is the angle between them anything but 0/180?? Regardless.. The graph has a slope of 3, therefore acceleration's x component is 3. Therefore net force x-component is 5.1 Therefore, 2.6cos(a) + 9.0cos(b) = 5.1 But so what? That's all the information that the problem gives me. Granted I know that cos(a) has to be between 1 and 0 for it to be in the positive direction... Any hints? I really have no idea!