first of all the diver is currently 200 feet below sea level. if the ship is pulling the diver at the rate of 25 feet per minute then 10 minutes ago,25×10= 250 feet. this means that 10 minutes ago the diver was 250 feet deeper than his current feet below sea level,then u add the two levels to get the final level the diver was 10 minutes ago
first level below sea level + new level obtained
=200+250
=450
finally the diver was 450 feet 10 minutes ago