$\text { The position vector } r ( t ) = \langle 7 t , 6 \cos t , 6 \sin t \rangle \text { describes the path of an object moving in }$

Multiple Choice

$\text { The position vector } r ( t ) = \langle 7 t , 6 \cos t , 6 \sin t \rangle \text { describes the path of an object moving in }$ space. Find the speed $s ( t )$ of the object.

A) 21
B) $3 \sqrt { 7 }$
C) $\sqrt { 93 }$
D) 149
E) $\sqrt { 85 }$