Answer
Please see the graph.
Work Step by Step
Before trading, consumer surplus is area $A$, and producer surplus is the sum of areas $B+C$. With trade, consumer surplus is now $A+B+D$, and producer surplus is $C$.
Prior to trade, total surplus was $A+B+C$. With trade, total surplus is $A+B+C+D$. Thus, the change in total surplus is $D$.
