b5=b1*q^4
b5=36*(1/3)^4=36*1/81=36/81=4/9
S=(b5*q-b1)q-1 =( 4/9*1/3-36)/1/3-1=(4/27 -36)/(-2/3)=((4-972)/27)/ -2/3 = (968/27)*3/2=2904/54=53 42/54
b5=b1*q^4
b5=36*(1/3)^4=36*1/81=36/81=4/9
S=(b5*q-b1)q-1 =( 4/9*1/3-36)/1/3-1=(4/27 -36)/(-2/3)=((4-972)/27)/ -2/3 = (968/27)*3/2=2904/54=53 42/54