Problem $4$: The shadow of a pendulum cast on a flat board moves on a straight line. By placing the $x-$axis on the straight line with the origin at the middle of the total path, the $x-$coordinate of the shadow is given by the following function: $x(t)=56cos(t),$ where $t$ is in seconds and $x$ is in centimeters. How much distance in centimeters does the shadow travel in $20$ seconds.