Hey! The other person is correct in saying 6, but I would like to explain a bit further :)
700 divided by 125 is 5.6. Unfortunately for this equation we can’t have 5.6 busses, meaning we have to round up. Because it is 5.6 we have to round up to 6 instead of 5, because if we round down we have to kick some people out which hasn’t been a method I have learned in math :)) this means 6 busses would do the job :)
I hope this helps, and have a great day <3