c. Write down the day of the month on which you were born (just the date, not the month or year). Multiply that number by 20. Double today's date and add it to your answer. Now, multiply this number by 5. Add the month of your birthday (e.g. March is 3, November is 11). From this result, subtract ten times today's date. The four-digit number you are left with represents your birthday. The date of your birthday first and the month at the end.