Connor made a graph showing the relationship between the day of the week he worked, Monday through Saturday, and the number of square feet of mulch he used. His graph covered one moth. Is the relationship represented by by Connor's graph a function?

Yes it is a function depending how he wrote it. Since it's safe to assume each day, he would use the same amount on every Monday he did or Tuesday or Wednesday etc etc.

So every X day he had Y amount of mulch up to his month of graphing. The question doesn't say anything about how he used less or more on any particular day. So it's a function.