Firms A, B, and C operate in the market for computers. Each firm's product is popular in the market and is distinct from what the other firms offer. The following table shows the prices of laptops from 2005 through 2007. 
Which of the following is the unweighted price index for the total price of three types of laptops in 2006, using 2005 as the base year?
Definitions:
Confounding Variable
An outside influence that changes the effect of a dependent and independent variable being examined in an experimental or observational study.
Independent Variable
A variable in an experiment that is manipulated or changed by the researcher to observe its effects on the dependent variable.
Covaries
When two variables change in relation to each other, suggesting a potential relationship or correlation between the two.
Double-Blind Procedure
A research or testing method in which neither the participants nor the experimenters know who is receiving a particular treatment, to prevent bias.
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