Name the number of cab size for 4 medium tanker
CREATE TABLE "table1_2155350_2" (
  "category" text,
  "sub_category" text,
  "cab_size" text,
  "drive_wheels" text,
  "capacity_litres" text
);
SELECT COUNT("cab_size") FROM "table1_2155350_2" WHERE "category"='4 Medium tanker';