b1=8
q=1.2
b2=8*1.2=9.6
b3=9.6*1.2=11.52
b4=11.52*1.2=13.824
b5=13.824*1.2=16.5888
S5=b5*q-b1/q-1
S5=16.5888*1.2-8/1.2-1=59.5328
b1=8
q=1.2
b2=8*1.2=9.6
b3=9.6*1.2=11.52
b4=11.52*1.2=13.824
b5=13.824*1.2=16.5888
S5=b5*q-b1/q-1
S5=16.5888*1.2-8/1.2-1=59.5328