You must convert ONE of the units of measurement, using a conversion factor, so that it's the same as that used in the other (surfboarder case).
Then you'll be comparing two speeds in meters per second or feet per second, but not both.
Look in your book or on the Internet for "meter." One or the other will tell you how many feet are in one meter. (It's approx. 3.1 feet = 1 meter, but you should be more accurate than that.
Now suppose you want to compare the 2 guys' speeds in meters per sec.
Mult. the speed given in feet per sec by the conversion factor.
(5 meters / sec) (3.1 feet / 1 meter).
Cancel out "meters" and "meter" and you'll have this person's speed in feet per second, so you can then immediately compare that to the other person's speed (which was already in feet per second).
