Well youcanuse the complement and it does make some calculations easier... you aren't finding the correct complement. Specifically you're interested in:

the trick to using the complement is to recall that if A is an event then (where is the complement of A)

so we're really looking for the complement of {X >= 38}. Well if we aren't in the set X >= 38 then that means that X must be less than 38 so the complement is {X < 38} so using this

Now if that actually helps depends on what you know and what you can calculate easily...