Refer to figures.
FLY-BY-WIRE (FBW)
A fly by wire system is a powered flying control system that uses electronic inputs to a solenoid operated servo valve rather than the mechanical inputs on conventional power controls.

The pilot operates the flight deck controls, which in turn operates transducers which convert the mechanical input into an electrical output which is amplified, processed by computers with the processed command signal providing the input to the servo valve which controls the movement of a hydraulic actuator.

The A320 is a typical example of an aircraft with a FBW system in which all surfaces are actuated hydraulically and are electrically or mechanically controlled.

SYSTEM REDUNDANCY
Safeguards to eliminate the possibility of loss of control in the event of hydraulic or electrical failure must be provided on modern transport aircraft. This is generally achieved by building some form of redundancy into the control system.

Splitting the control surfaces into two or three sections, each powered by separate actuators and hydraulic systems is the usual method. The A320 (EASA's usual favourite aircraft) has 2 actuators per aileron aswell, an active and a "damping", which can be used in the event of the failure of the active.

Important Note: This question is far too ambiguous about the aircraft in question and the fault that has occured. We have to go to the level of the learning objectives, and try to see what the examiner wants from us. They want us to know that there are multiple computers for each system, so in this event, the system can switch computers, and redundancy in the rest of the system allows us to use a different actuator aswell. This is not true for all FBW aircraft, but going off the feedback, this is what EASA want from us.