Expected Payoff of Max Difference of Dice

You and I each roll a fair six-sided die, getting values $X$ and $Y$ respectively. Your payoff is $\max(X - Y, 0)$. (a) Give an 80% confidence interval for how much you would pay to play this game. (b) Calculate the exact expected payoff $E[\max(X - Y, 0)]$. (c) You can switch your fair die to a non-standard die with faces $\{1, 1, 1, 6, 6, 6\}$. Should you switch? (d) Instead, you can switch **my** (the opponent's) die to the $\{1, 1, 1, 6, 6, 6\}$ die. Should you make this switch?