Initial data: Q (the amount of heat that the machine received to perform the work) = 4 kJ; A (amount of work done by the machine) = 1 kJ.
The efficiency of a machine can be defined as the ratio of the perfect work to the amount of heat received for its implementation: η = A / Q.
Calculation: η = 1/4 = 0.25 or 25%.
Answer: The efficiency of the heat engine is 25%.
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