Answer:
(1)
(2)
If we divide equations (2) and (1) we got:

And then 
And then we can find the value
and we got from equation (1)

And then the general term for the sequence would be given by:

And the best option would be:
C) a1=759,375; an=an−1⋅(1/15)
Step-by-step explanation:
the general formula for a geometric sequence is given by:

For this case we know that 
Then we have the following conditions:
(1)
(2)
If we divide equations (2) and (1) we got:

And then 
And then we can find the value
and we got from equation (1)

And then the general term for the sequence would be given by:

And the best option would be:
C) a1=759,375; an=an−1⋅(1/15)