Answer: f = 4.67 Hz
Explanation:
We can approximate the wave as a traveling wave, therefore the speed of the wave is constant
v = d / t
the total distance remember, in going to the wall and back is
d = 2 11.2 = 22.4 me
we substitute
v = 22.4 / 4.0
v = 5.6 m / s
now we can use the relationship between the speed of the wave, its wavelength and u frequency
v =λ f
f = v /λ
f = 5.6 / 1.2
f = 4.67 Hz
