What is the Col entry for the peak with an elevation of 2,308 meters?
CREATE TABLE "list_of_ultras_of_africa" (
  "peak" text,
  "country" text,
  "elevation_m" real,
  "prominence_m" real,
  "col_m" real
);
SELECT COUNT("col_m") FROM "list_of_ultras_of_africa" WHERE "elevation_m"='2,308';