a. Given a calendar for any month of the year, such as the one that follows, pick severa...

a. Given a calendar for any month of the year, such as the one that follows, pick several 3 x 3 groups of numbers and find the sum of these numbers. How are the sums obtained related to the middle number?

b. Prove that the sum of any nine digits in any set of numbers selected from a monthly calendar will always be equal to 9 times the middle number.