Which is a property of bases?

What property is a characteristic of a substance that can be observed and does not change the identity of the substance

Light from the sun reaches the earth in 8.3 minutes. the velocity is 3.00 x 10^8 m/s. how far is earth from the sun? i know how to get to d = (3 x 10^8 m/s)(498 sec). i just don't know how to get from there to the answer being 1.5 x 10^11 m.

Mechanical energy is when the amount of kinetic and potential energies added together remains the same. conserved created lost