The way I did this was determine the proofreaders’ page/hour rate. 200/6 is 33.33, while 200/9 is 22.22. 55.55 in total. 55.55/hour, combined, means that this hourly rate would need to multiply to fit in three hours. Thus, we multiply 55.55 by three, giving us 166.65. This is not two hundred, meaning you need more time, or better proofreaders.