To find the price that maximizes Regina's revenue, we need to determine the vertex of the quadratic equation given by \( y = -0.5x^2 + 24x \).
The vertex \( x \) of a parabola described by the equation \( y = ax^2 + bx + c \) can be found using the formula: \[ x = -\frac{b}{2a} \] In this case, \( a = -0.5 \) and \( b = 24 \).
Plugging in these values: \[ x = -\frac{24}{2 \times -0.5} = -\frac{24}{-1} = 24 \]
Thus, the price at which Regina should sell her book to achieve maximum revenue is $24.
The correct response is: $24