I need someone to go over and correct my answers please, I was haveing trouble on these three.

What is the wave speed for a wave of 5 meters wavelength that has a frequency A) 25.6 m/s.
B) 64 m/s.
C) 128 m/s.
D) 640 m/s.
I think its a

A string on a guitar is 0.4 m long and produces 360 Hz as its fundamental tone. If you press on the string so that you reduce its free length to 0.2 m, what tone will it produce?

A) 270 Hz.
B) 480 Hz.
C) 540 Hz.
D) 720 Hz.
I think it is D

You have a tuning fork that produces a frequency of 512 Hz in air. You submerge it in the swimming pool and strike it against the wall underwater. The speed of sound in water is 1500 m/s. What will the resulting frequency and wavelength be?

A) 740 Hz, 3.41 m
B) 740 Hz, 0.773 m
C) 512 Hz, 3.41 m
D) 512 Hz, 2.93 m

I Think it is D

Or help me figure out how to solve it