All the answers here! The main goal in 100 Doors is to escape the room. Using all the possibilities of the device you need to open each of 100 doors and move the doors to the next Level.
Search for hidden objects, solve puzzles and use an items to do this!
Tap the puzzle on the door. Move the pieces to the empty cell. Complete the image.
This level is very hard until you understand the concept on how to move the pieces correctly.
I don’t have a lot of advice for you except that the missing piece is the bottom right one. Which means that you need to start by doing your top row.
Start by putting your top left and top right corner in place then work on placing the two top one. After, complete your left row. When these 2 are complete, you have the same puzzle but 3×4 instead of 4×4. Try to repeat what you just did with the final pieces
Most of the pieces, especially in the end the to be assembled in the correct order before putting them in the place. Most pieces must be put 2 at the same time.
Sorry if this isn’t clear but I don’t have a lot of advice.
Here is the final image