Answer:
The amount of medicine in Elizabeth's blood is the highest at t = 2.5 hours.
Work:
To find the time when the amount of medicine in Elizabeth's blood is the highest, we need to find the maximum value of the function M(t) = -t² + 5t.
We know that the maximum value of a quadratic function occurs at its vertex. The x-coordinate of the vertex of a quadratic function in the form of ax² + bx + c is given by -b/2a.
In this case, a = -1 and b = 5, so the x-coordinate of the vertex is -b/2a = -5 / 2(-1) = 2.5.
Therefore, the amount of medicine in Elizabeth's blood is the highest at t = 2.5 hours.