An arithmetic series has common difference 2 . The 3rd, 6th and 10th terms of the arithmetic series are the respective first three terms of a geometric series
a + (n-1) d
a + 2 *2 = b = a + 4
a + 5 *2 = b r = a + 10
a + 9 *2 = b r^2= a + 18
so
br - b = 6
b r*2 - b r = 8
b = 6 / (r-1)
b = 8 / [r(r-1)]
6 / (r-1) = 8 / [r(r-1)]
6 = 8/r
r = 4/3 etc
or continuing form Anonymous'
a+4, a+10, a+18 as the AS terms
(a+10)^2 = (a+4)(a+18)
a^2 + 20a + 100 = a^2 + 22a + 72
a = 14
so the first 3 terms of the GS are 18, 24, and 32
with an r value of 24/18 = 4/3