What is the Upper index Kcal/ Nm 3 of iso-butane, and a Lower index MJ/ Nm 3 smaller than 84.71?
CREATE TABLE "wobbe_index_of_common_fuel_gases" (
  "fuel_gas" text,
  "upper_index_kcal_nm_3" real,
  "lower_index_kcal_nm_3" real,
  "upper_index_mj_nm_3" real,
  "lower_index_mj_nm_3" real
);
SELECT COUNT("upper_index_kcal_nm_3") FROM "wobbe_index_of_common_fuel_gases" WHERE "fuel_gas"='iso-butane' AND "lower_index_mj_nm_3"<84.71;