What is the total in the case where theere are 6 lecturers and fewer than 48 professors?
CREATE TABLE "ntua_academic_staff_per_school" (
  "lecturers" real,
  "associate_professors" real,
  "assistant_professors" real,
  "professors" real,
  "total" real
);
SELECT AVG("total") FROM "ntua_academic_staff_per_school" WHERE "lecturers"=6 AND "professors"<48;