Speed of wave is given as
[tex]v = 5 m/s[/tex]
Wavelength of the wave is given as
[tex]\lambda = 20 m[/tex]
now from the formula of wave time period we can say
[tex]speed = \frac{wavelength}{time period}[/tex]
[tex]5 = \frac{20}{T}[/tex]
[tex]T = \frac{20}{5}[/tex]
[tex]T = 4 s[/tex]
so it will have time period of T = 4 s
