The Displacement from Equilibrium of an Object in Harmonic Motion $y = \frac { 1 } { 6 } \cos 12 t - \frac { 1 } { 2 } \sin 8 t$

The displacement from equilibrium of an object in harmonic motion on the end of a spring is $y = \frac { 1 } { 6 } \cos 12 t - \frac { 1 } { 2 } \sin 8 t$ where $y$ is measured in feet and $t$ is the time in seconds. Determine the velocity of the object when $t = \pi / 8$ . Round your answer to two decimal places.

A) $8.00 \mathrm { ft } / \mathrm { sec }$
B) $4.68 \mathrm { ft } / \mathrm { sec }$
C) $6.00 \mathrm { ft } / \mathrm { sec }$
D) $1.00 \mathrm { ft } / \mathrm { sec }$
E) $5.00 \mathrm { ft } / \mathrm { sec }$