What is the total decile in the area of Normanby with a roller smaller than 157?
CREATE TABLE "south_taranaki_district" (
  "name" text,
  "years" text,
  "area" text,
  "authority" text,
  "decile" real,
  "roll" real
);
SELECT SUM("decile") FROM "south_taranaki_district" WHERE "area"='normanby' AND "roll"<157;