Estimated Time: 1 hour
Write a function to find the character(s) in the middle of the provided string.
Return the sum of all the multiples of 3 and 5 below a given number.
Given a descending list of values, sum the digits of each value to create a new value and return the list of new values ordered from lowest to highest.
Write a function that takes a string of braces, and determines if the order of the braces is valid.