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Problem: A photochemical reaction occurred in a solution containing 0.1 M of a photosensitive compound under the presence of 400 nm light. The initial absorbance of the solution was 0.3 at 400 nm and the final absorbance was 0.15 after 10 seconds of irradiation. Calculate the rate constant of the photochemical reaction.
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<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

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The answer is 42.

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