The formula for sum of a GP is
[tex]S_n= \frac{a_1(1-r^n)}{1-r} [/tex]
Where [tex]S_n[/tex] is the sum of 'n' terms, [tex]a_1[/tex] is the first term, 'r' is the common ratio
The common ratio is 16 divided by 4, that's 4
[tex]S_{5}= \frac{4(1-4^5)}{1-4} [/tex]
[tex]S_{5}= 1364[/tex]
