Hi, and welcome!
First, for future questions, you should be familiar with the forum's homework policy, and pay special attention to the key role that reproducible examples, called a reprex play in helping to troubleshoot a specific problem.
Here's a checklist for this type of problem.
- What is the unknown necessary to calculate the result?
- If none of the columns is the unknown, can you calculate the unknown from two or more of them?
- Once you've identified the unknown, what function is necessary to calculate the result?
- Is the result the same or different if you group the data by other variables.
- (Possibly extra credit to your assignment.) What is the probability that the observed differences are due to chance?