How would I do this problem?

Use the formula a[sub-1]+a[sub-1]r+a[sub-1]r[squared]+...+a[sub-1]r[n-1 power]=

a[sub-1]* 1-r[nth power]/1-r

for the nth partial sum of a geometric sequence to find the sum 1+2/3+4/9+8/27+...+64/729.

possible answers:

701/2187

2059/729

2187/701

2187/729