Let S1 & S2 be the sample spaces of two sub experiments. The considered sample space S is .a O s1 X S2 b o S1 + S2. .c O S1/S2 d O S1- S2. The expected value of x (m2) if the density of the random variable X is fx(X) = 3 (-x+12x-32)/32 {u(x-4) - u(x-8)} a O 16.8 24.5 .cO 36.8 d O none of these