Calculus related rates problem with acceleration! please help!

Hi, I'm currently in calculus and I don't know how to do this problem on my homework, we've been doing related rates but this one has acceleration in it and we havnt done any like it in class so I was confused. The question is: Water is leaking out of a conical tank with a velocity of -729pi in/min and an acceleration of -324pi in/min. The diameter of the top of the tank is 40 in and the height of the tank is 90in. What is the acceleration of the depth of the water when the water is 18in deep?