Question 3 Censider the following \"mindreading" trick. Come up with a 3 digit integer, call it n. Then shufe anyway you like the digits of r, to come up with the integer 3;. Then nd |m y|, and determine the three digits, say a, b, c that represent the resulting positive number. Then any two of the digits can reveal the third digit, almost always, since one can show that n: + h + c E [1(mod9). For example, if two of the digits were, say in = the = 9, then the third one is e such that a. + 13 = I}[mod9). Because a, is a digit between 0 and 9, the answer was 5. One occasion that is problematic is whenever I; + c E Dmon) in which case a could be either I] or 9. Find the formal proof that explains why a + b + c E 0(mod9)