user: Question: What is the Upper index Kcal/ Nm 3 of iso-butane, and a Lower index MJ/ Nm 3 smaller than 84.71?
Columns: ['Fuel gas', 'Upper index Kcal/ Nm 3', 'Lower index Kcal/ Nm 3', 'Upper index MJ/ Nm 3', 'Lower index MJ/ Nm 3']
Types: ['text', 'real', 'real', 'real', 'real']
Sample row: ['Hydrogen', 11528.0, 9715.0, 48.23, 40.65]
SQL:

assistant: SELECT "Upper index Kcal/ Nm 3" FROM "Table" WHERE "Fuel gas" = 'iso-butane' AND "Lower index MJ/ Nm 3" < 84.71;