How do you find the apothem of a shape??

I'm pretty sure it's b). i try drawing the functions out and b is the one that stands out or isnt a "line"

38+105= 143, 39+104=143, and you will find then adding the numbers on opposite sides, moving inwards yields the answer 138 every time. because of this, you’re going to multiply 138 times the number of pairs, which is 34. therefore, 34*138= 4692(i’m sorry if it’s the wrong numbers, but it’s the right concept)