Momentum before ejection P_b:
P_b= (M+m)*v_M=8*500=4000, since the package is still on the satellite and isn't moving.
Momentum after ejection P_a:
according to the law of conservation of momentum P_b=P_a, and this gives me:
4000=450*8 + v_m*50 => (4000 - 3600)/50 = v_m = 8 km/s
But according...