Einstein did not precisely calculate the speed of light. He postulated that the speed of light in vacuum, measured by a non-accelerating observer, is independent of the motion of the source or observer. In other words, the speed of light is a constant. Einstein left the measurement of the speed of light to others.Einstein’s answer in the comic is excellent because it would be impossible to know how fast he was going…in absolute terms. It would be the velocity of the vehicle relative to the road, plus the rotation of the earth, plus the orbital velocity of the earth around the sun, plus the velocity of the solar system relative to other stars in the Milky Way, plus the velocity of the Milky Way relative to other galaxies, plus the expansion of the universe….