Final answer:
The amount of medicine in Elizabeth's blood is modeled by a quadratic function. The medicine is at its highest concentration 10 hours after she takes it.
Step-by-step explanation:
The amount of medicine in Elizabeth's blood is modeled by the function m(t) = -t² + 20t, where t is the number of hours. To determine when the medicine is at its highest concentration, we need to find the maximum value of the function.
To find the maximum value of a quadratic function, we can use the formula t = -b/2a, where a and b are the coefficients of the quadratic equation. In this case, a = -1 and b = 20, so we have t = -20/(2*(-1)) = 10.
Therefore, the medicine is at its highest concentration in Elizabeth's blood 10 hours after she takes it.