Parameter estimation

#1
Hi
I have analyzed dependent and independent variable for 4 products and come up with an estimate for the 5th product using linear regression
y=mx+c.
Don't worry about the "y" variable. so I have y variable for all the 5 products. x variable in the above equation has been obtained using some parameter weights and scoring criteria below.

So for examples for all the 4 products and even the 5th one:-
Parameter Weights Scores
Market size 60% 5
Cost of therapy 30% 4
Disease characteristic 5% 2

and so on for other parameters
So x= 60%*5+30%*4+....

I would like to know given this, how can I find my weights and what theory should i apply in statistics to see how closely are the numbers (60%, 30% etc.)