Question

If 3.0 kilograms of gasoline were burned in a car engine, they would yield 140,000,000 joules, which is a tremendous amount of energy. However, burning the gasoline only produces a chemical change. Convert those 3.0 kilograms of gasoline completely into energy, using Einstein's equation. (1 J = 1 kg m2/s2)

Answer 1

e = mc^2

Answer 2

Correct. You are going to see that 140,000,000 is not that much after all compared to the total energy. Evaluate the following expression and you are good to go.
\[E=3.0 ~ kg \times \left( 299,792,458 ~ \frac{ m }{ s } \right)^{2}\]
Notice that the units is correct for joule.