Decorating

Last week, my next-door neighbour asked me, "Seeing as our houses are the same design, can I ask how many rolls of wallpaper you bought to decorate the living room?"
"Thirteen," I said.
Today, he came around looking angry. "I've got three rolls left over!"
"Thirteen," I said.
Today, he came around looking angry. "I've got three rolls left over!"
Spoiler: