A patient is to be given a mixture of two drugs Xeniccilin and Yasprin. Each of these drugs causes the body temperature of the patient to change. When x milligrams of Xeniccilin and y milligrams of Yasprin are given the temperature of the patient is f(x, y) degrees farenheit. Suppose that initially the ptaient is given 30 mg of Xeniccilin and 20 mg of Yasprin and that this combination does not affect the patient's body temperature. (a) What is the practical significance of the facts that (30,20)=0.3 and (30,20)=−0.6? (b) If the dosage of Xeniccilin is increased by a small amount, 1.7 milligrams, how much should the dosage of Yasprin be changed in order that the patient's temperature does not change?