A relatively small impact crater 20 kilometers in diameter could be made by a

A relatively small impact crater 20 kilometers in diameter could be made by a comet 2 kilometers in diameter traveling at 29km/s (2.9×104m/s ).

Part A

Assume that the comet has a total mass of 4.2×1012 kilograms. What is its total kinetic energy? (Hint: The kinetic energy is equal to 12mv2, where m is the comet's mass and v is its speed. If you use mass in kilograms and velocity in m/s, the answer for kinetic energy will have units of joules.)
Express your answer using two significant figures.

K = joules

Part B

Convert your answer from part A to an equivalent in megatons of TNT, the unit used for nuclear bombs. Comment on the degree of devastation the impact of such a comet could cause if it struck a populated region on Earth. (Hint: One megaton of TNT releases 4.2×1015 joules of energy.)
Express your answer using two significant figures.

K = megatons