no need to show work. just tell me which answer

If R denotes the reaction of the body to some stimulus of strength x, the sensitivity S is defined to be the rate of change of the reaction with respect to x. A particular example is that when the _ brightness x of a light source is increased, the eye reacts by decreasing the area R (square millimeters) of the pupil. A formula used to model the dependence of R on x is: R(x) = (40 + 24 x^(2/5)) / (1 + 4 x ^(2/5)). The sensitivity can be found by the derivative S = dR/dx = R' (x). This derivative can be found by ... O. applying the Quotient Rule on the overall problem and the Power Rule in individual derivatives, such as R' (x) = [(1 + 4x ^(2/5))*(24 (2/5) x^(-3/5)) - (40 + 24 x^(2/5))*(4 (2/5) x ^(-3/5))] / (1 + 4 x ^(2/5)) ^ 2, and then simplifying O "cancelling" the x^(2/5) in the original function, and then reducing R(x) (40 + 24)/(1 + 4) to 64/5, which is a constant having derivative R ' (x) = 0 O dividing the derivative of the numerator by the derivative of the denominator with the use of the Power Rule, such as R ' (x) = [24 (2/5) x^(-3/5)] / [4 (2/5) x ^(-3/5)], and then simplifying O dividing the derivative of the denominator by the derivative of the numerator with the use of the Power Rule, such as R ' (x) = [4 (2/5) x ^(-3/5)] / [24 (2/5) x^(-3/5)], and then simplifying