Well when you think about this, if 7 people are walking, you can automatically take them out of the total. So you have 318 people who are taking busses. Now take that 318 and divide it among 7 busses. So 318/7 = 45.4285714286. Now looking at this, logically you can't put half a person on one bus and half a person on another, you can't have 1/4 of a person on your bus. So this means some busses would carry 1 more than others. So logically each bus would have to be able to hold 46 people.