Answer
The answer and procedures of the exercise are attached in the following archives.
Explanation
A. The superiority of d3 will vanish when EMV of d2 will be equal to 15. Let that happen at payoff under strong demand for d2 be Ds2 so that
Ds2*0.8 + 3*0.2 = 15 or, Ds2 = 14.4/0.8 = 18
Check the excel attached.
So, The payoff for the medium complex under strong demand remains less than or equal to $18 million, the large complex remains the best decision.
B. Similarly, The superiority of d3 will vanish when EMV of d1 will be equal to 15. Let that happen at payoff under strong demand for d1 be Ds1 so that
Ds1*0.8 + 7*0.2 = 15 or, Ds1 = 13.6/0.8 = 17
So, The payoff for the small complex under strong demand remains less than or equal to $17 million, the large complex remains the best decision.