This will tell you how many cubic feet you need. Whether you need it more or less might depend on the size of the mulch pieces. More finely ground mulch pieces require less depth.

The total volume of the booth is then 63 cubic feet. Assuming the average weight of the 33 students to be 140 pounds (a very conservative estimate), we see that the students weigh 4620 pounds, or ...

The Mazda CX-30 is pretty much a lifted Mazda3 hatchback. Same platform, awfully similar dimensions, and the interior's a spitting image (if not identical).