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A transformer has a primary coil with 150 turns and a secondary coil with 300 turns. The primary coil carries a current of 5 A. Calculate the magnetic field in the core of the transformer assuming that it has a length of 20 cm, a cross-sectional area of 5 cm², and a permeability of 4π × 10⁻⁷ H/m.
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<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

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<|begin_of_solution|>

The answer is 42.

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