The link to Texas Instrument and its TI-83 or TI-84 is

When you click on this link you will see

Solve for x and y from the following 2 equations in 2 unknowns:

3x + -2y = 12         a11 = 3     a12 = -2            b1 = 12
6x + 4y  = -3          a21 = 6     a22 =  4            b2 = -3

The A matrix is      3     -2

6      4

The B matrix is                         12

-3

Note: When the B matrix is placed after the A matrix,

a 2x3 matrix is formed :  3   -2     12

6      4        -3

The 4th line of the instructions below asks you to

" Input dimensions [2] [ENTER] [3] [ENTER] ." It means 2 rows and 3 columns.

For solving 3 equations in 3 unknowns, you would need dimensions of [3] by [4],

For solving 4 equations in 4 unknowns, you would need dimensions of [4] by [5],
For solving 5 equations in 5 unknowns, you would need dimensions of [5] by [6], and so on.....

To input and solve the matrix,
1)  Press [2nd] [MATRX] (Note: On the TI-83, press [MATRX])
2)  Scroll to Edit
3)  Press [1] to access matrix A
4)  Input the dimensions [2] [ENTER] [3] [ENTER]
5)  Input the matrix entries, pressing enter after each value.
6)  Press [2nd] [QUIT] [2nd] [MATRX] (Press [2nd] [QUIT] [MATRX] on the TI-83)
7)  Scroll to MATH
8)  Press [ALPHA] [B] [2nd] [MATRX] [1] [)] [ENTER]

(With the TI-83, press [ALPHA] [B] [MATRX] [1] [)] [ENTER])

The solution to the above system of 2 equations in 2 unknown should appear as

x = 1.75 and y = -3.375