From 1.
(1)
From 2.
(2)
(3)
From 3.
(4)
(5)
(4) + (3) {w/Ng}
(6)
(6) + (5) { }
(7)
(1) + (4) {x/Ng}
(8)
(8) + (5) {y/M}
(9)
(9) + (7) { }
Therefore Ng is happy.