What was the MNZ FEA when the SIL SPR was 18?
CREATE TABLE "teams_championship" (
  "team" text,
  "car_no" text,
  "mnz_spr" text,
  "mnz_fea" text,
  "spa_spr" text,
  "spa_fea" text,
  "mon_fea" text,
  "sil_spr" text,
  "sil_fea" text,
  "hun_spr" text,
  "hun_fea" text,
  "lms_spr" text,
  "lms_fea" text,
  "cat_spr" text,
  "cat_fea" text,
  "points" text
);
SELECT "mnz_fea" FROM "teams_championship" WHERE "sil_spr"='18';