(r1 * 4 + r2)
(r1 * -2 + r3)
(r1 * 3 + r4)
= (-1 0 3 -2)
(0 1 12 -3)
(0 -3 -5 10)
(0 3 5 -5)
--------------------
(r3+r4)
= (-1 0 3 -2)
(0 1 12 -3)
(0 -3 -5 10)
(0 0 0 5)
---------------------
(r2 * 3 + r3)
= (-1 0 3 -2)
(0 1 12 -3)
(0 0 31 1)
(0 0 0 5)
= -155