Motion Equations for Constant Acceleration in One Dimension (Problem 21)

A well-thrown ball is caught in a well-padded mitt. If the deceleration of the ball is $2.10\times {10}^4{\text{ m/s}}^2$, and 1.85 ms $(\text{1 ms}={10}^{-3}\text{ s})$ elapses from the time the ball first touches the mitt until it stops, what was the initial velocity of the ball?