`1+3+3^2+...->n` terms
Here, first term, `a = 1` and common ratio, `r = 3`.
`:. S_n = (1(3^n-1))/(3-1)`
`:. (3^n-1))/(3-1) gt 7000`
`=>3^n -1 gt 14000`
`=>3^n gt 14001`
Now, `3^8 = 6561`
`3^9 = 19683`
So, minimum value of `n` for which `3^n` is greater than `14001` is `9`.
`:. n = 9.`
