Hello there!
Answering this question, we are to answer the question, but not necessarily as a full answer. We will end the answer as a variable, as that's what the question is asking.
Let s = students ; let b = buses
234s-12s = 222s/6b
We did 234 student subtracted by the amount traveling by car. Which would equal 222 students divided by the amount of buses, which would be 6.
Your answer: 234s-12s = 222s/6b