What is the maximum energy of the Λ particle after the Σ0 baryon decay?

[ElectricEel1]

i had 0.034c as the velocity of the lambda in the sigma rest frame. then using 2gev as the energy of the sigma in the lab frame, I calculated the momentum and used the relativistic momentum equation to find the sigma velocity. Then I used u' = (u-v)/(1-uv/c^2) to where u = 0.034c and v = 0.69c (sigma velocity in lab frame) to get the lambda velocity and then the energy. Or should I have used u = (u' + v)/(1 + u'v/c^2) since I am transforming from a rest frame to the actual lab frame

 

[mfb]

One will lead to a value that doesn't make sense, the other one is the right answer.