From the decision tree, Expected Value $($EV$)$ of Sell idea alternative $=5\mathrm{.}5$

EV of Large plant $=0\mathrm{.}7*(0\mathrm{.}6*15+0\mathrm{.}4*4)+0\mathrm{.}3*(-2)=6\mathrm{.}82$

EV of Small plant, Don't expand $=0\mathrm{.}7*(0\mathrm{.}6*10+0\mathrm{.}4*6)+0\mathrm{.}3*3=6\mathrm{.}78$

EV of Small plant, Expand $=0\mathrm{.}7*(0\mathrm{.}6*12+0\mathrm{.}4*4)=6\mathrm{.}16$

Recommended strategy: We see that EV of Large plant is the highest.

Therefore, the best alternative is to open the Large plant

c$)$ Resulting Payoff $=$ $ $6\mathrm{.}82$ millions