The correct choice is (c) 0.536
For explanation: 1-(overline{X_{(B)}}) = 0.5((frac{τ}{overline{t}}) – frac{1}{3!}(frac{τ}{overline{t}})^2+frac{1}{4!} (frac{τ}{overline{t}}))^3-…, as obtained by expansion.
1-(overline{X_{(B)}}) = 0.4635 and (overline{X_{(B)}}) = 0.536