12 + 10h = 8h + 4
12 + 10h = 4 + 8h
12 + 10h = 4 + 8h
12 + 10h + -8h = 4 + 8h 10h + -8h = 2h
12 + 2h = 4 + 8h + -8h
8h + -8h = 0
12 + 2h = 4 + 0
12 + 2h = 4
12 + -12 + 2h = 4 + -12
12 + -12 = 0
0 + 2h = 4 + -12
2h = 4 + -12
4 + -12 = -8
2h = -8
h= -4
h = -4