Think about it this way, you cannot do something positive and then do something negative and it still be positive. You cannot do something negative and then do something positive for it to be positive. But you can do something positive and do something else positive for it to remain positive the same with negative. Therefore the answer is "negative."
4*25= 100. There are 26 tables. At each of the 25 tables 4 people are sitting. Which means 100 people are sitting in complete tables of 4 people. That means that at the 26th table 3 people are sitting. 103-100= 3. Hope that helps. :)
