Confusion about week 2 exercise 5

Suppose that the augmented matrix for a linear system has been reduced by row operations.
just like this example:
|1 -3 4 7|
|0 1 2 2 |
|0 0 1 5 |

assume the variables range from x1 to x3
to get the answer of all the variables is to use process called back substitution.
start from the last row and check x3 and associated value which is now x3 = 5 and then go the middle row and then since you have x3, find x2.
x2 = 2 - 2(x3)
x2 = 2 - 10
x2 = -8
lastly you can find easily x1 using the same path, that is what questions needs you to do, and in code you have to figure it using list slice and indices.

I hope that clarifies your questions.
Let’s know the progress.