Answer:
He will have brownies for 1189 days before he runs out
Explanation:
So first we need to find the area of the brownie pan that the brownies are in and to do that the formula and length times width times height so we will multiply 20, 29 and 41 which gives us 23780 square centimeters. That is how much total brownie Marc has and since he eats 20 square centimeters each day we will divide that number by 20 to figure out how many days he will have brownies for 23780/20=1189
I hope this helps and please don't hesitate to ask if there is anything still unclear!