You beat me to the punch. I sat down and calculated with the measuring tool available on the website and tried to roughly measure all the mowable areas. It came out to be 22.9 acres.
The big patch of sand? I guess you're looking at the football field which has gone dormant.
Anyway, the area right in the front of the school along the highway. You see the big L shaped drive coming off the Hwy, that whole huge section that runs the length in front of the school (from red line to red line) is 12 acres of open turf. The remaining acreage came from the back and sides of the school.
I can vouch that the tool is reasonably accurate because where I live is one acre, and the measure tool recorded 1 acre on the line I drew.