Find the Radian Measure of the Central Angle of a Circle

Multiple Choice

Find the radian measure of the central angle of a circle of radius $r$ that intercepts an arc of length $s$ .
radius: $r = 12$ kilometers arc length: $s = 64$ kilometers

A) $\frac { 3 } { 16 }$
B) $\frac { 3 \pi } { 16 }$
C) $\frac { 16 \pi } { 3 }$
D) $\frac { 8 } { 3 }$
E) $\frac { 16 } { 3 }$