Answer to Question 1
With chocolate on the vertical axis and vanilla on the horizontal, as you move rightward along your indifference curve, the more chocolate you give up and the less you have remaining. As a result, you grow to value your chocolate more and more and your vanilla less and less. You therefore become willing to give up less chocolate to get more vanilla.
Answer to Question 2
The second executive's work is simply the value of the next best opportunity which is the work that could have been done by the third executive which is 500,000