Hello,
\(u_{1}=72\\
u_{2}=\dfrac{72}{6}\\
u_{3}=\dfrac{72}{6^{2}}\\
u_{15}=\dfrac{72}{6^{14}}\\
s=72*(1+\dfrac{1}{6^{1}}+\dfrac{1}{6^{2}}+\dfrac{1}{6^{3}}++...+\dfrac{1}{6^{14}})\\
=72*(\dfrac{\frac{1}{6^{15}}-1}{\frac{1}{6}-1}})\\
=72*(\dfrac{470184984576-1}{78364164095*5})\\
=86,400...\)
