Custom function for budget costs

/**
 * Calculates the total annual amount of an expense
 * by multplying its amount by it's frequency.
 * 
 * @param {number} amount - dollar cost of an expense.
 * @param {number} frequency - annual, monthly, or weekly.
 * 
 * @returns {number} - annual cost
 */
function ANNUAL_COST(amount, frequency) {
  return amount * timesPerYear(frequency);
}

/**
 * @param {string} frequency - frequency as a string.
 * 
 * @return {number} - number of times per year.
 */
function timesPerYear(frequency) {
  switch (frequency) {
    case '1 time':
      return 1;
    case 'Weekly':
      return 52;
    case '2 weeks':
      return 52 / 2;
    case 'Monthly':
      return 12;
    case '2 months':
      return 6;
    case 'Semester (6 months)':
      return 2;
    case 'Yearly':
      return 1;
  }
}