First: make a sketch or drawing of your question
second : label the given value of a each part
third:  form it a right triangle
1500 = which is the height of of a right triangle
29° = the angle of depression of the triangle 
  then you can be able to solve the distance between the plane and the rock by using the SOH CAH TOA . in this case we used the TOA.

tan 29° =opposite/ 1500
opposite or the distance = 831. 46 (rounded off to the nearest hundredths)