SOLUTION
 Dependent variables are those variable that rely on other variables to find their value.
Independent variables are those variabe that do not rely on other variables to find their value.
Hence, an independent variable will change the value of a dependent variable, but a dependent variable cannot change the value of an independent variable, and the value of the dependent variable is determined by the value of the independent variable.
From the illustration given in the question, 

Hence 
The amount paid is dependent on the distance he travelled
Therefore 
The dependent variable is The Amount Paid
Option A is correct