b1+b5=30
b3+b7=b1q^2+b5q^2=(b1+b5)q^2=120
q^2=120/30=4
b1+b5=b1+b1q^4=b1(1+q^4)=30
b1(1+16)=30
b1=30/17
b1+b5=30
b3+b7=b1q^2+b5q^2=(b1+b5)q^2=120
q^2=120/30=4
b1+b5=b1+b1q^4=b1(1+q^4)=30
b1(1+16)=30
b1=30/17