Physics question - phase difference

[Leeum]

Hi,

Having a little difficulty in doing this question:

A wave of frequency 5 Hz travels at 8 kms–1 through a medium. What is the phase difference, in radians, between two points 2 km apart?

A 0
B Pi/2
C Pi
D 3Pi/2

I understand the phase difference is (2Pi/Wavelength) x (X1-X2). This leaves me with the answer 7.85 which I assume is an angle - degrees? How do I convert that to Radians/ relate it to Pi.

Cheers

 

[Leeum]

I understand radians but I cant get my head around that question. The answer is supposedly B.