Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Fuel gas | Upper index Kcal/ Nm 3 | Lower index Kcal/ Nm 3 | Upper index MJ/ Nm 3 | Lower index MJ/ Nm 3 |
| --- | --- | --- | --- | --- |
| Hydrogen | 11528.0 | 9715.0 | 48.23 | 40.65 |
| Methane | 12735.0 | 11452.0 | 53.28 | 47.91 |
| Ethane | 16298.0 | 14931.0 | 68.19 | 62.47 |
| Ethylene | 15253.0 | 14344.0 | 63.82 | 60.01 |
| Natural gas | 12837.0 | 11597.0 | 53.71 | 48.52 |
| Propane | 19376.0 | 17817.0 | 81.07 | 74.54 |
| Propylene | 18413.0 | 17180.0 | 77.04 | 71.88 |
| n-butane | 22066.0 | 20336.0 | 92.32 | 85.08 |
| Iso-butane | 21980.0 | 20247.0 | 91.96 | 84.71 |
| Butylene-1 | 21142.0 | 19728.0 | 88.46 | 82.54 |
| LPG | 20755.0 | 19106.0 | 86.84 | 79.94 |
| Acetylene | 14655.0 | 14141.0 | 61.32 | 59.16 |
| Carbon monoxide | 3060.0 | 3060.0 | 12.8 | 12.8 |
Question:
What is the Upper index Kcal/ Nm 3 of iso-butane, and a Lower index MJ/ Nm 3 smaller than 84.71?
Answer:
0.0