4th and 7 terms of a G.P. are 1/18 and -1/ 486 respectively. Find the G.P.

Question

My solution:
ar^3=1/18.... eq no1
ar^6=-1/486...eq no2
ar^6/ar^3 = -1/486÷1/18
r^3=-1/27
r=-1/3
Place this value in equation 1
ar^3=1/18
a*-1/3^3=1/18
a*-1/27=1/18
a=-7/6
Required GP:
a=-7/6
ar=-7/6*1/3=-7/18
-7/6,-7/18.......n =ans
My answer is not correct please tell me the correct answer

Answer 1

a*-1/27=1/18
a=-7/6

Bzzzt.

a = -3/2