Answer:
0.091 m/s
Step-by-step explanation:
Given in the question that,
wavelength of a wave = 7mm
frequency of a wave = 13 hertz
Formula to use
f = v / λ
here f = frequency in hertz
v = velocity in m/s
λ = wavelength in m
1 mm = 1x10

7mm = 7x10

Plug values in the formula
13 = v / 7x10

v = 13(7x10^{-3})
v = 0.091 m/s