Solution to Problem 3

First, find the inverse of matrix B, which is $\left[ \begin{array}{rrr} 8&-5&-2\\ 7&-4&-2\\ -18&11&5\\ \end{array}\right]$

Then, divide the incoming numbers into groups of three, form $3\times 1$ vectors, multipuly each vector by the inverse of matrix B. You will get the following string of numbers:

16 18 15 6 9 19 2 15 18 9 14 7

Converting these to letters, the message reads

P R O F I S B O R I N G

So the message decodes to "Prof Is Boring."