The square would be 100.
The semicircle you will use the formula πr^2/2.
That would mean you would take the 3.14x5^2/2.
(3.14x5x5)/2
(3.14x25)/2
78.5/2
=39.25
So the total area would be 139.25
The answer would look something like this:

There could also have a simplified version.
I hope this helps.
Answer: each 1/3 would be 4 brownies.
Step-by-step explanation: 12 divided by 3 is 4.