Answer:
r=3 where r is the common ratio
Explanation:
The sum of geometric progression for n terms is given by:
, where
is the
first term of the series and r is the common ratio.
Now, according to the question, there are four terms and they form a geometric progression. So sum of four terms is given as
and
.
Also according to the above formula:

Using the values as given in the question into the above equation we get:


[ Using formula
]




which is the required answer.