Question 853828
Tn = t * r^(n - 1)
30 = t * r^(1)+t * r^(3),
90 = t * r^(5)-t * r^(1)
r = 2,   t = 3
Tn = t * r^(n - 1)
T8 = 3 * 2^(7)
T8 = 384