Physics Work,Power & Energy Level: Misc Level

(no pciture) A 0.024 kg bullet is fired straight up at a falling wooden block that has a mass of 3.0 kg.The bullet has a speed of 670 m/s when it strikes the block. The block originally was dropped from rest from the top of a building and had been falling for a time t when the collision with the bullet occured. As a result of the collision, the block (with the bullet in it) reverses direction, rises, and comes to a mo0mentary halt at the top of the building. Find the time t.s