How far away is the rock face? (Wavelengths)

[WhyHello]

1. A submarine sonar system sends a burst of sound with a frequency of 325 Hz. The sound waves bounces off an underwater rock face and returns to the submarine in 8.50s. if the wavelength of the sound wave is 4.71 m, how far away is the rock face? The answer is 6.51 x 10^3m.


I keep trying this question different ways but the only thing that I believe I'm doing correct so far is:
v=f$$\lambda$$
v=(325Hz)(4.71m)
v=1530.75m/s
I also know that 8.50s must be divided in two, so that it will equal 4.25s.
Than I go to solve how far away is the rock...
v=$$\lambda$$/T
$$\lambda$$=vT
$$\lambda$$= (1530.75m/s)(4.25s)
$$\lambda$$= 6505
Never mind i figured out that i made a calculator error. Sorry ):

 

[Redbelly98]

Glad it worked out. Welcome to Physics Forums!

By the way, if you use [noparse][itex]instead of $$[/noparse], it won't put the symbol on a new line all by itself. Or, for "λ", you can just copy-and-paste from the symbols list at the bottom of this post.$$[/itex]