The difference between 63y and 35y is 28y. 28/2=14, 28/4=7, 28/7=4, 28/9=not whole number so I'm not doing the math, and to make sure we are right, 28/14=2
How many students would there be? did not see that information if that is the question but if not I say go with the bus that has more seats yes it is more expensive but more space is better!