C1_W2 - Row Echelon form in general - Wrong Row Echelon form

Hello,

I am a bit confused about this one:

a + b + 2c = 12
3a - 3b -c = 3
2a - 1b - 6c = 24

The matrix
1 1 2
3 -3 -2
2 -1 6

In the lesson is said the row echelon form of the matrix is
1 1 2 = 12
0 -6 7 = -33
0 0 6 = 18 (getting 16.5 here)

From my calculation c is not 18 but 16.5 because the last row for me is
0 0 5.5

Am I doing something wrong?

Thanks
Carlo

Your -2 in the 2nd row of the matrix is incorrect. It should be -1.