Interference and slits question

[doctordiddy]

Homework Statement

A radar tower sends out a signal of wavelength . It is meters tall, and it stands on the edge of the ocean. A weather balloon is released from a boat that is a distance out to sea. The balloon floats up to an altitude . In this problem, assume that the boat and balloon are so far away from the radar tower that the small angle approximation holds.

Due to interference with reflections off the water, certain wavelengths will be weak when they reach the balloon. What is the maximum wavelength that will interfere destructively?

What is the maximum wavelength that will interfere constructively

http://session.masteringphysics.com/problemAsset/1010843/27/98393A.jpg

Homework Equations

The Attempt at a Solution

I'm not quite sure what to do, I know that for these questions you typically want to find deltad. I'm assuming once you find deltad you can equate it to lambda/2 (destructive interference) and then multiply the deltad by 2 to get lambda? So I guess my problem is I'm not sure how to find the deltad and how to tell whether it is the maximum wavelenght or not. Can anyone help me out/give me tips?

thanks

ps the answer is for part a is 2x(h/d), i don't know how to get there however..

 

[ehild]

Find the yellow and orange pathlengths in terms of the position (y) where the ray reflects from water in terms x, h, d, from the right triangles you find in the figure.

ehild