I've been on the hunt for a book and tape from the early 90s that had vinyl reusable decals. It was about two kids on a hunt for a surprise from their grandpa. Along the way, they had to solve math problems and you would have to stick the decal with the answer into the scene. You could then turn the tape to the other side and go through the book in reverse on a hunt for "Double O". Anyone else hear of it?