Final answer:
The room service waitress receives a 15% gratuity, as stated in the equation.
Step-by-step explanation:
The gratuity percentage the room service waitress receives can be determined by looking at the equation g = 0.15b.
In this equation, 'g' represents the gratuity and 'b' represents the food bill.
Since the coefficient 0.15 is equivalent to 15%, it means that the room service waitress receives a 15% gratuity. Therefore, the correct answer is B. 15%, because it's stated in the equation.