17
5th term = 140
7th term = 35
We have that
(140)r^2 = (35) where r is the common ratio
Divide both sides by 140
r^2 = 35/140 = 1/4 take both roots
r = +/- sqrt (1/4) = +/- 1/2
So....note that the 6th term could be (140)(1/2) = 70
Or.....the 6th term could be (140) (-1/2) = -70
Thus..... ± 70 is correct