There are 2 formulae you will need to use in this question, v=f*lambda where f is the frequency and lambda is the wavelength. The second one is f=1/T where f is the frequency and T is the time.
Firstly, let's work out f:
f=1/(4*10^-1)=2.5Hz
Then, we can substitute it into the second equation to work out the speed:
v=2.5*(1*10^-2)=0.025= 2.5*10^-2 m/s