Super Mario Bros. 3 Question

[SushieBoy]

I've heard that in the game you can find 4 number "3's" I found one in 1-1 and another in the World two world map, but I can't find the others! Can anybody tell me where to find them? Maybe provide some screenshots if possible?

[Deezer]

In World 5-1, fly up from where you start into the pipe. Take the lower path and you'll be inside the dome. Fly straight up and hit the P-switch to reveal two giant 3's made out of coins. [P-Wing recommended for all the flying]