In Exercises 40 through 49, assume that the required extreme value is a relative extremum.

Consider an experiment in which a subject performs a task while being exposed to two different stimuli (for example, sound and light). For low levels of the stimuli, the subject’s performance might actually improve, but as the stimuli increase, they eventually become a distraction and the performance begins to deteriorate. Suppose in a certain experiment in which x units of stimulus A and y units of stimulus B are applied, the performance of a subject is measured by the function f(x, y) = C + xye^1−x2−y2 where C is a positive constant. How many units of  each stimulus result in maximum performance?