If the equation for volume is V=l*w*h, you can plug in all of the information you know. When you do this, the equation becomes 1440=15*12*h, or 1440=180*h (because 15*12=180). You can divide both sides by 180 to get h. 1440/180=8, do the depth of the pool is 8 ft. You can also check this answer by making sure that 15*12*8 is equal to 1440 (which it is). I hope this helped!