How Does the Lorentz Transformation Affect Observed Velocity?

[Camilla]

If an observer O' see a body that moves with constant velocity U_x along the axis x' in a positive direction. What is the velocity V_xO of body observed by O?
That is all the information I have.
Can you help?

 

[vela]

There's not enough information to solve that problem. You need to know the velocity of O' relative to O.