Answer:
-8mph
It is not possible for Sarah to have a speed of -8 mph, as speed is a scalar quantity and cannot be negative. Speed is defined as the magnitude of velocity, which is a vector quantity that has both magnitude and direction. A negative speed would indicate that the direction of Sarah's motion is opposite to what is stated. It is likely that you meant to ask about Sarah's velocity, which could be -8 mph. But since the question does not specify her direction, it is impossible to give an accurate answer.
Explanation: