Starting with the 2nd term divide each term by the preceding term:

15/5 = 3
45/15 = 3
135/45 = 3
405/135 = 3

Since they are all the same, that shows that it is a geometric series 
with first term a1 = 5, common ratio r = 3, and number of terms n = 14.

The formula for the sum Sn of a geometric series with first 
term a1, common ratio r, and number of terms n is:



Plugging in a1 = 5, r = 3, and n = 14 into the formula:



You simplify that.  The answer is an 8-digit number

Edwin