This allocation is Pareto efficient: it is the allocation associated with the competitive equilibrium in which the price is $2.
(b) Allocation after trade:
units of good, amount of money
payoff
X
0,$2
$2
Y
0,$3
$3
A
1,$2
$7
B
1,$3
$5
This allocation is not Pareto efficient: it is dominated by the allocation in part (a), in which A is better off and the other three people have the same payoff as they do here.