The operation we are using to replace Row 2 is R₂3 R₁, that is,

Bottom minus 3 times Top.

Working from left to right, we get

(Bottom)3(Top)
3 3(1) = 0
5 3(5) 5 + 15 = 20
5 3(2) = 1

Therefore, the new bottom row is

[0201]

and the matrix becomes

	1	5	2
	0	20	1