I am having difficulties trying to find out the missing dimensions of a cutout piece. Can someone please tell me how to figure out the dimensions. They've given me the dimensions for the whole solid, but just not the cut out piece. Your help will be appreciated :-)

MISSING DIMENSION ROUND TO NEAREST TENTH..

QUESTION; THE SCALE OF A MAPIS 3in =6.82 mi map :_________ in
actual 2.3 mi