3x1 + 6x2 -24x3 =21 | :3
-10x1 -19x2 + 71x3 = -96
-3x1-3x2-2x3 = -95
<=>
x1 + 2x2 -8x3 =7
-10x1 -19x2 + 71x3 = -96 | +10* erste
-3x1-3x2-2x3 = -95 | + 3*erste
<=>
x1 + 2x2 -8x3 =7
x2 -9x3 = -26
3x2-26x3 = -74 | -3*zweite
<=>
x1 + 2x2 -8x3 =7
x2 -9x3 = -26
x3 = 4
Also x3=4