What is the area of one of the semicircles at either end of the track

Afactory adds 3 red drops and 2 blue drops of coloring to white paint to make each pint of purple paint. the factory will make 50 gallons of the purple paint. how many drops of red and blue coloring will the factory need in the 50 gallon batch of purple paint.

Can someone check if i did this correct. it’s number 4 if you’re wondering.

I'm confused on this could anyone me and show me what i need to do to solve it.