How hard can it be ?

As players entered the room one cold Thursday night, they were confronted with a problem on the whiteboard.  Amanda's boss was building a retaining wall and wanted to know how much concrete to order for the 36 post holes.  Some had very simple solutions, but once Henry, a maths professor, entered the room, his eyes lit up and he was in his element.  Away he went and with stunning speed, had the formula on the board for all to see.  Of course we all understood this and the actual amount required at the bottom right corner.

Good thing Amanda took a photo and presented it to her boss.  He had to be impressed, but did he ever find out how much concrete he needed do you think ?