TIP
This is a G P Geometric Progression
The first term a is 8
The common ratio is 1/6
in this case the ratio is less than 1
[tex]\begin{gathered} r=\text{ }\frac{t_2}{t_1}=\frac{t_3}{t_2} \\ r=\text{ }\frac{3}{18}=\frac{1}{6}\text{ } \\ S=\frac{a(1-r^{n)}}{1-r}\text{ where r<1} \\ \text{where a=8 , r=}\frac{1}{6}\text{ and n=8} \\ S_8=\frac{8(1-(\frac{1}{6})^8)}{1-\frac{1}{6}} \\ S_8=\frac{8(0.9999)}{0.8333} \\ S_8=\frac{79999}{0.8333} \\ S_8=9.60037\approx10\text{ nearest interger} \end{gathered}[/tex]