Finding the width of a diffraction slit

[theskyisgreen]

Homework Statement

Single-slit diffraction can be observed with any type of electromagnetic wave (not just light). Suppose you want to make a diffraction slit whose width is seven times larger than the wavelength for the following cases. How wide would the slit be?

(a) A radio wave for your favorite FM station (f = 100 MHz)


(b) The waves that carry your cell phone signals (f = 2.0 GHz)


(c) Red light (f = 5e14 Hz)


(d) The X-rays used in your dentist's office (f ≈ 4e20Hz)

Homework Equations

The Attempt at a Solution

I honestly have no idea where to begin with this.
I do know that the answer to a) is 7*3.. but I don't know why?
If anyone can point me in the right direction it would be appreciated.

 

[Mindscrape]

The relationship between frequency and wavelength is

$$\lambda=\frac{c}{f}$$

where c is the speed of light. The problem has nothing to do with diffraction.