There is a power up hidden among the top row of bricks, just left of center. If you are small, it is unreachable, and you can only collect six of the coins.
Because this coin room is exclusive to World 3-1, you should successfully collect the mushroom before coming down here.
To access the coins at the top, break the bottom two blocks in either the right most or left most columns.
Super Mario can access the coins along the bottom just like regular Mario can. You just need a running start from the left, and push down to make Mario slide.
You can also use a running start to pick up a Fire Flower, but don't smash any of the highest level of the ceiling/floor before this.
The right most block above the pipe entrance has 10 coins hidden inside.
To access the coins above the bricks, jump on the right most block, and then jump left to cross the ceiling. From the ceiling, jump to the top of the left wall, and then take a small hop to the right, in to the gap.
If you are super-sized, it is also possible to break the wall on the right of the boxed coins. Do this if you can't jump from the left as described in the step above.
Hop on top of the flat cloud platform, and jump forward to collect the coins. If you accidentally fall off, accelerate to pass the cloud, and jump on from the right.