Answer :
I would use the starting position, sea level as zero. Then I would convert all those minutes to hours so the answer is an integer and not a decimal.
60 min * (-10 ft / 212 min) = -2.83 ft/hr
round to integer = -3 ft/hr
60 min * (-10 ft / 212 min) = -2.83 ft/hr
round to integer = -3 ft/hr