Verified answer

q>1,

b1+b2+b3=7,

b1*b2*b3=8;

b1+b1q+b1q^2=7,

b1*b1q*b1q^2=8;

b1(1+q+q^2)=7,

b1^3*q^3=8;

(b1q)^3=2^3,

b1q=2,

b1=2/q,

2/q * (1+q+q^2)=7,

2+2q+2q^2=7q,

2q^2-5q+2=0,

D=9,

q1=1/2<1,

q2=2.

b1=1.

b5=b1q^4,

b5=1*2^4=16.