How to compute "weight"? Assume I have a list of 100 used cars, which the following information for each: year, make, model, mileage, selling price. How could I figure out how much does the year, make, model, and mileage affect the cars selling price?

Is there a program that'll do this? If someone can explain the math to me - or at least point me in the right direction, maybe I can write a simple program to figure this out myself.
Have considered using regression analysis?
Have considered using regression analysis?