Could someone please answer this

Omar is going on a road trip! the car rental company offers him two types of cars. each car has a fixed price, but he also needs to consider the cost of fuel. the first car costs $90 to rent, and because of its fuel consumption rate, there's an additional cost of s0.50 per kilometer driven.

How do you solve a question like this?

Arectangle has a width of 5 cm and a length of 10 cm. if the width is increased by 3, how does the perimeter change?