A firm started advertising its product and this changed the product's elasticity from -2 to -1.5. If, prior to advertising, the firm was maximizing profit by charging $10, the firm should?

a. raise the price from $10 to $15

b. reduce the price from $10 to $6.67

c. raise the price from $10 to $13.33

d. reduce the price from $10 to $7.50