Hello Kittyhacker14! :) I am Grace Rosalia, and I hope my answer wil help you!
First, we must calculate 15% of 300.
We do this like this:
300:100=3
Now we multiply it by 15:
3*15=45
So 15% of 300 is 45. (that's how many students arrive on foot)
Now we must compute how many students arrive by bus (it's done like that:
300*3/5=180 (that's how many students arrive by bus)
Now we must calculate how many students arrive by car.
That's how it's done:
300-180-45=75
So 75 students arrive by car.