How to make a calculation on the site?

Question

JavaScript

The task is to add a calculation to the site. The conditions of this calculation are as follows:

Choice cost: 1000 rubles per hour per person. When adding the number of working hours, the cost should change to the following values: 2-3 hours - 600 rubles per hour per person, 4-6 hours - 500 rubles per hour per person. Cost calculation: the number of people multiplied by the number of hours and multiplied by the number of working days. When changing select, the price should change, but the calculation principle should not change. Please tell me how to implement this correctly, nothing comes out in my code :(

My experience: https://codepen.io/kiskiskit/pen/XWmRvbJ