Learn how it works first, go here.
Ok this is the system:
x1 + x2 + 2x3 - x4 = 4
x1 + 3x2 - 3x3 - x4 = 1
2x1 + 3x2 + 3x3 + x4 = 8
3x3 - 7x3 + x4 = -4
I need to solve it, and I am guessing its done by row operations, but I cant realy understand how its done.