Calculus - please show detail explanation. thanks!

The sales of a product, S = f(p, a) (in hundreds of dollars) is a function of the price, p, of the product (in dollars per unit) and the amount, a, spent on advertising (in hundreds of dollars). a. What do you expect fp to be? O Negative O Need more information O Positive Zero Explain why? Put your answer in the answerbox. Edit * Insert * Formats . B / U X X A A E wr - b. Explain the meaning of fa (8, 12) = 150 in the context of the given situation. Put your answer in the answerbox