12x+108 = 180
12x = 180-108
12x = 72
x = 72:12
x = 6

4z+12x+56 = 180
4z+72+56 = 180
4z+128 = 180
4z = 180-128
4z = 52
z = 52:4
z = 13

56+5x+2y = 180
56+5.6+2y = 180
56+30+2y = 180
86+2y = 180
2y = 180-86
y = 94:2
y = 47

2x+y+z = 2.6+47+13
2x+y+z = 12+47+13
2x+y+z = 72°

Jawaban: D