$2\mathrm{.}4.**$ Establish $(2\mathrm{.}6)($a$)$ by setting up suitable portfolios and applying the argu$-$

ments used to get $(2\mathrm{.}4)-(2\mathrm{.}5),$ and $($b$)$ separately, by using $(2\mathrm{.}4)-(2\mathrm{.}5)$ plus

put$-$call parity $(2\mathrm{.}2).$