Find the Position Vector of a Particle That Has the Given

Short Answer

Find the position vector of a particle that has the given acceleration and the given initial velocity and position.
$$\mathbf { a } ( t ) = - 4 \mathbf { k } , \mathbf { v } ( 0 ) = \mathbf { i } + \mathbf { j } - 20 \mathbf { k } , \mathbf { r } ( 0 ) = 4 \mathbf { i } + 9 \mathbf { j }$$