Step 1: Identify the puzzle pieces.
Each puzzle piece contains part of a digit, and the correct arrangement of the pieces forms the number. Arrange the pieces based on their visual alignment.
Step 2: Form the number.
After rearranging the pieces, the four-digit number formed is:
\[
\boxed{4127}.
\]
Final Answer:
\[
\boxed{4127}
\]