parameters with multiple values and summing them for a bar chart

hi,

I have a query that takes in multiple parameters, some of which can have many values.

I know that I can check for the values in the where clause : where carType = (@cartype),

but what if I want to sum the value of cartype ?    Should I create a temporary table and then loop through it to sum up and display all the

different values?  I'm not sure what the best and most efficient method is. 

thanks