Momentum of particle a under radical sign: 2*4*Ea
Conservation of recoil momentum
Po momentum: 2*4*Ea under the root sign.
Po kinetic energy: (2*4*Ea)/(2*2 18)
Formula: E= Delta ·mc^2
Ea+(2*4*Ea)/(2*2 18)= Delta mc^2.
Simplify to get Δ m, which is a quality defect.
No compromise is C.