$\"\"$

Time taken by diana to complete the puzzle $\"\"$ hrs i.e., $\"\"$ pre hr.

Time taken by ella to complete the puzzle $\"\"$ hrs i.e., $\"\"$ per hr.

Together they can complete in $\"\"$

They can complete in $\"\"$ per hr.

Time $\"\"$ taken to complete one full puzzle is $\"\"$ .

$\"\"$

The correct answer is $\"\"$ .