Speak to Penny Dreadful, who is standing close to the cloud station on Whisperwind Isle. ( -510, 0, -460 ) /waypoint -510, 0, -460
Talk to banker Drevious located in the Windgazer's Hideout near Polly ( -682, 4, -545 ) /waypoint -682, 4, -545. He tells you that he mistakenly gave gold for platinum and platinum for gold, but you need to figure out how much they originally had.
Return to Penny and tell her the original amount was 18 pp and 56 gp. (last choice)