If R(t) Is the Position Vector of a Particle in the Plane

Multiple Choice

If r(t) is the position vector of a particle in the plane at time t, find the indicated vector.
-Find the acceleration vector.
$\mathbf { r } ( t ) = ( 8 \ln ( 9 \mathrm { t } ) ) \mathbf { i } + \left( 3 \mathrm { t } ^ { 3 } \right) \mathbf { j }$

A) $a = - \frac { 8 } { t ^ { 2 } } i + 18 t j$
B) $a = \frac { 8 } { t ^ { 2 } } t ^ { - 2 } i + 18 t j$
C) $a = \frac { 8 } { t } i + 9 t j$
D) $\mathbf { a } = - \frac { 8 } { 9 } \mathrm { t } ^ { - 2 } \mathbf { i } + 18 \mathrm { t }$