Find the Length of an Arc of a Circle of Radius

Multiple Choice

Find the length of an arc of a circle of radius $12$ ft if the arc subtends a central angle of $135 ^ { \circ }$

A) $s = \frac { 3 \pi } { 4 } \mathrm { ft }$
B) $s = 12 \pi \mathrm { ft }$
C) $s = \frac { 9 \pi } { 8 } \mathrm { At }$
D) $s = 9 \pi \mathrm { ft }$
E) $s = 12 \mathrm { f }$