*pre-calc test, probably a trig question though*

Hi, i took a math test today and there was a bonus at the end and i was wondering what anyone thinks (i had a double period of math and the bonus took about a full one. if you didnt want to do the bonus you could have gone to the cafeteria but i wanted to try it). so the question went something like(it was a pic): the lengths of a baseball field from home plate all the way down the left and right sidelines is 300 ft. home to first and home to third is 90 ft(obviously leaving 210 for the remainder of the sideline). from home straight down the middle all the way is 400ft. and what we had to try and do was find the best length for the back curve of the field. if anyone can help id appreciate it, im very curious.