A manufacturing company has three workers, Grace, Henry, and Irene, who are assembling a batch of 1200 electronic gadgets. Grace takes 25 seconds to assemble one gadget, Henry takes 18 seconds, and Irene takes 20 seconds. If Grace and Henry both assemble all 1200 gadgets, Henry will spend how many fewer seconds assembling than Grace?
7200
8000
8400
9600
10800
