We are given with a sequence, which is a GP (Geometric Progression), as the ratio [tex]{\bf{a_{n+1}:a_{n}}}[/tex] is 1/3 for every [tex]{\bf{n\in \mathbb{N}}}[/tex], so 1/3 is the comman ratio r, and we needa find sum till 6 terms, so n = 6, and first term is 6, so putting all the values we will be having ;
[tex]{:\implies \quad \sf S_{6}=\dfrac{6\bigg\{1-{\bigg(\dfrac13\bigg)}^{6}\bigg\}}{1-\dfrac13}}[/tex]
[tex]{:\implies \quad \sf S_{6}=\dfrac{6\bigg(1-\dfrac{1}{3^{6}}\bigg)}{\dfrac{3-1}{3}}}[/tex]
[tex]{:\implies \quad \sf S_{6}=6\bigg(\dfrac{3^{6}-1}{3^{6}}\bigg)\div \dfrac23}[/tex]
[tex]{:\implies \quad \sf S_{6}=6\bigg(\dfrac{3^{6}-1}{3^{6}}\bigg)\times \dfrac32}[/tex]
[tex]{:\implies \quad \sf S_{6}=\dfrac{3^{6}-1}{3^{4}}}[/tex]
[tex]{:\implies \quad \sf S_{6}=\dfrac{3^6}{3^4}-\dfrac{1}{3^4}}[/tex]
[tex]{:\implies \quad \sf S_{6}=3^{2}-\dfrac{1}{81}}[/tex]
[tex]{:\implies \quad \sf S_{6}\approx 9-0.012\approx 8.988\approx \boxed{\bf{8.99}}}[/tex]