To study the effectiveness of air purifiers in removing smoke, engineers ran each purifier in a smoke-filled 10 ft x 20 ft room. In the accompanying figure, the function f gives the rate of change of the smoke level per minute, t min after the start of the test, when a Brand A purifier is used. The function g gives the rate of change of the smoke level per minute when a Brand B purifier is used. Find an expression for the area of S in terms of a definite integral involving f and g. Ay (%/min) a b 1 (min) y =f(0) S y =g(1) S = Select--- v dt a