Explanation:
a geometric series means that
sn = sn-1 × r
with r being a constant for the whole series.
so,
s1 bring the starting value, we get
s2 = s1 × r
s3 = s2 × r = s1 × r × r
s4 = s3 × r = s2 × r × r = s1 × r × r × r
we see,
sn = s1 × r^(n-1)
in our case
s1 = 14
n = 6 and n-1 = 5 :
s6 = 448 = 14 × r⁵
r⁵ = 448/14 = 32 = 2⁵
therefore,
r = 2