Elements in the same row,column location combine, and that number is placed in the answer matrix
in that row column location. Note: If both matrices don't have the same dimensions,the
operation is undefined.

To multiply, start at the left element in the row you need and the
top element in the column you need. Multiply those together. Keep going.Add all the products together. Place
that number in the matching row column of the product matrix.Note: If the number of columns in the
first matrix doesn't match the number of rows in the second, they cannot be multiplied together.

Convert letters to number equivalent. I'll do HELP, which is 8 5 12 16. Organize that into
a matrix with the same number of columns as the key matrix dimension. I'll use a 2 by 2 key, so my
message is in a 2 column matrix. Multiply the message times the key to encode the message.
In this example: 34 47 68 96.

Organize the encoded message into a matrix with the same number of columns as the key. Multiply
that by the inverse of the key matrix and you will have the original message back. Here, 8 5 12 16.

To write the augmented matrix,each row is an equation. Each column gets the
coefficient of a single variable (first column x's, second column y's,etc). If a variable
is not in the equation, put a zero as the coefficient. The rref command on the calculator
will provide reduced row echelon form of the augmented matrix.

To get the reduced echelon form, use ref in the math menu of matrix. To solve, start at the bottom.
Here, z = 5. Then substitute the 5 in for z in the equation above it. Here, y + 2(5)=13. That will allow
you to solve for y. Then substitute the number values for y and z into the top equation to solve for x.
You should get x=6, y=3 and z=5 for this example.