I'm suppose to solve for x, but my textbook never covered how to solve this:

| 5x - 8 1 |. | 2 1 |
| 3 4m - 1| = | 3 7m+ 6|
Can someone please help me ?

just multiply the matrices

Unfortunately, you have not provided all the elements
Go through the mechanics, and you will wind up with a column matrix containing expressions involving x.
Equate each row of the column and then solve for x.
It's hard to format matrices here. Try writing them as nested vectors, such as
(3 4)
(-2 7)
would be ((3,4),(-2,7))
so we can see what each row contains.