**Answer:**

348643.34 barrels of oil

**Explanation:**

Given;

Volume of the granite = 1 km³ = 1000³ m³

Specific heat of granite, C = 790 J/kg.°C

Density of granite = 2700 kg/m³

Energy in 1 barrel of oil = 6.118 × 10⁹ J

For every 1° change in temperature, ΔT = 1°C

Now,

The thermal energy stored is given as;

Thermal energy = mCΔT

where, m is the mass

the mass of 1 km³ of granite = Density × Volume

or

the mass of 1 km³ of granite = 2700 × 1000³ = 27 × 10¹¹ Kg

therefore,

Thermal energy = 27 × 10¹¹ × 790 × 1

or

Thermal energy = 21330 × 10¹¹ J

hence,

the thermal energy in terms of barrels of oil

= Total thermal energy / Energy stored in 1 barrel of oil

= 21330 × 10¹¹ J / ( 6.118 × 10⁹ J per barrel )

= **348643.34 barrels of oil**