I cant really give any concrete help not knowing about the environment but I'll write something
If you know the resistance over the distance and the current flowing through then the voltage-drop is U = R * I
The resistance of copper cable can be solved by R = 0.0175 * l (lowercase) / A
If you know all the influential resistance values of the circuit (in series) you can solve the question as voltage-drop is linear to the resistance of the component.
This one's more of an electronics solution, requires basic knowledge of electronics.
U = voltage
R = resistance
I = current
l (lowercase) = length
A = area
+8 
