The linear function that models the total cost \( f(x) \) of renting a car, where \( x \) is the number of miles driven, can be expressed as:
\[ f(x) = 0.50x + 50 \]
Here, \( 0.50x \) represents the cost incurred for driving \( x \) miles ($0.50 per mile), and the $50 is the base charge for renting the car itself.