Add back/forward buttons to my car rental booking system

Simple 30 minute job which I'm too busy to do myself, I have an application built in MySQL and PHP, it's a car rental booking system with the following stages: 1. choose date 2. choose car 3. choose extras 4. total cost 5. booking details 6. payment 5 and 6 are not always required depending which car they choose on step 2, this in an extra stage so their are 7 pages in total. We need a backwards and forwards button adding to each of these pages, we also need the system to retain all data and options they select in each of these stages - most of this data is already stored into the session and I wrote this myself so are positive this will be very easy. You will also need to keep in style with the coding standard of this application and I will be checking your work after so no exceptions. Will give URL of this system to potential developers via PMB. International providers welcome so long as you have good English skills, payment will be deposited into escrow and released when work is finished.