Instruction: Given the title, description, feature, price, and brand of a product and a set of target attributes, extract the value of each target attribute from the product information. Output the extracted value and the corresponding source (e.g., title or feature) denoting where the value is extracted.

Input:
Product title: Dell XPS 8700 X8700-4382BLK Desktop (Black) (Discontinued by Manufacturer)
Product description: Own the fastest XPS mini tower ever. With 4th Gen Intel Core processors that perform 15% better than the previous generation, you can blaze through system-intensive applications like video editing, HD video playback, serious multitasking and extreme gaming.
Product feature: Intel Core i7-4770 Processor 3.9 GHz, 16GB DDR3, 2 TB 7200 rpm Hard Drive, 32 GB Solid State Drive
Product brand: Dell
Target attributes: Number of Cores
Answer: attribute: number of cores
value: None
source: None