Instruction: Using the product's title, description, features, price, and brand, identify and retrieve the values associated with a specified set of target attributes. Output the extracted values along with their respective sources (e.g., title or feature) indicating where each value was found.

Input:
Product title: Cuarto Mariachi Guitar Complete Package by La Playa
Product feature: Spruce Top; Celluloid bound fingerboard & body, Rosewood fingerboard & bridge, Beautiful hi-gloss, richly grained walnut back and sides, Preamp/Pick-up; Nylon Gig Bag, Love it or return it within 15 days in new condition for an instant refund
Product brand: Windpony
Target attributes: Number of Strings
Answer: attribute: number of strings
value: None
source: None