a8=a1+12*7
54=a1+84
54-84=a1
a1=-30
a2=-30+12=-18
a3=-30+12*2=-6
a4=-6+12=6
a5=6+12=18
a6=18+12=30
a7=30+12=48
a8=a1+12*7
54=a1+84
54-84=a1
a1=-30
a2=-30+12=-18
a3=-30+12*2=-6
a4=-6+12=6
a5=6+12=18
a6=18+12=30
a7=30+12=48