Ok, I'll try to give a few hints:
You know that the boron was at rest, before the decay, that means by conservation of momentum:
\vec{p_C}=-\vec{p_e}
this means especially, that the momenta of carbon and electron have the same absolute value.
Since the energy is conserved (and we know the Boron was at rest, which means it had only it's rest Energy E=m_B c^2):
m_B c^2=E_e+E_C
now you plug in E^2=p^2c^2+m^2c^4 for e and C and use that the momentum for e and C hast the same absolute value(which I will denote by p):
m_B c^2 =2 p^2 c^2 +(m_e^2+m_C^2)c^4
Now you can use this to find p^2, since you now all the other quantities. then you plug this into:
p^2=\gamma^2 m^2 v^2
now you can plug in the formula for gamma and find v. (the speeds will be different for electron and Carbon since they have different masses).
To find E_{kin} you just plug p into E^2=p^2c^2+m^2c^4 for the electron and the Carbon, take the square root of it and substract m c^2 to get the kinetic energy
