What is the velocity of de Broglie wave?

Here is my calculation:
 note: $ν$ – frequency, $V$ – velocity of wave, $v'$– velocity of object. 
$$
\begin{align}
λ &= h/mv' \tag{1}\\
mc^2/h &= ν \tag{2}\\
λν &= V \quad \text{(wave equation)} \tag{3}
\end{align}
$$


Substituting 1 and 2 in 3 we get:


$$h/mv' \cdot mc^2/h = V$$


Simplifying we get:


$$c^2/v' = V$$


However, according to the book, the answer is $hv/mc$.
What is wrong with my answer? 




I think the problem arises partially from the confusing notations.
"Velocity of wave" $V$ is essentially $c$, "velocity of object" $v'$ is usually denoted with the speed of particle $v$ and the energy of photon $E$ is for some reason expressed via mass–energy equivalence $E = mc^2$ when it should be just kinetic energy of the particle $E = mv^2/2$ (but the latter is anyways irrelevant here).


So, your equation turns into this:


$$c^2/v' = V$$
$$c^2/v = c$$
$$c = v$$


which just states that the velocities of both wave and particle are equivalent.
I suggest you just combine the de Broglie equation


$$λ = \frac{h}{mv}$$


and the relation between wavelength $λ$ and frequency $ν$


$$λ = \frac{c}{ν}$$


so that 


$$λ = \frac{h}{mv} = \frac{c}{ν} \quad \implies \quad v =\frac{hν}{mc}$$


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