Question 580625
For a simple pendulum:

{{{T=2*pi*sqrt(L/g)}}}

T=8 seconds

g=9.8m/s2

{{{8=2*pi*sqrt(L/9.8)}}} 

{{{sqrt(L/9.8) = 4/pi}}}

{{{L/9.8 = (4/pi)^2}}}

{{{L = 9.8 * (4/pi)^2}}}

L = 15.9 m