Create a function that returns the average of a list composed of letters. First, find the number of the letter in the alphabet in order to find the average of the list.
A = 1
B = 2
C = 3
D = 4
E = 5
average = total sum of all numbers / number of item in the set
Return the result rounded to two decimal points.
average_index(["a", "b", "c", "i"]) ➞ 3.75
average_index(["e", "d", "a", "b", "i", "t"]) ➞ 6.83
average_index(["y", "o", "u", "a", "r", "e", "t", "h", "e", "b", "e", "s", "t"]) ➞ 12.62
Letters given will always be lowercase.