Needs help for a dynamics problem

How can I proceed for to solve this problem below.
Note: This problem came from the "kinematics of particles" part holding the "Determination of the motion of a particle" section, so use the formulae relating to this section of this part.

The asking problem:
A projectile enters a resisting medium at x = 0 with an initial velocity Vo = 900 ft/s and travels 4in. before coming to rest. Assuming that the velocity of the projectile was defined by the relation
V = Vo - kx, where V is expressed in ft/s and x in feet, determine the initial acceleration of the projectile.

The answer of this problem for your verification is:
-2.43 x 10^6 ft/s^2