Answer:
The  angle of depression from Platform A to Platform B is 
Step-by-step explanation:
Refer the attached figure 
The horizontal distance between the  platforms is 500 feet i.e. BC = 500 
 The length of the zip-line is 685 feet i.e. AB = 685
We are supposed to find the  angle of depression from Platform A to Platform B 
Hypotenuse = 685 
Base = 500 

Hence  the  angle of depression from Platform A to Platform B is 