The second line is obtained by subtracting the second line from the third line.

0 λ- 10 5 1

0 -2 1 λ+ 12 3

1 10 -6 1

Then, the line 1 is multiplied by -3 and added to the second line to get it.

0 λ- 10 5 1

0 -3(λ-3) λ-3 0

1 10 -6 1

Therefore, when λ-3=0, that is, λ=3, the rank is 2.

In other cases, the rating is 3.