The internal energy of the thermodynamic system, consisting of an air fire, a piece of cotton wool and liquid vapor

The internal energy of the thermodynamic system, consisting of an air fire, a piece of cotton wool and liquid vapor, increased by 10 mJ. What is the work of external forces equal to if the thermodynamic system did not receive energy from the outside and did not give it away?

Because the system is thermally insulated, then:
U = A (external) = 10 mJ

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