Answer
$-394.0\ kJ/mol$
Work Step by Step
From the definition of heat capacity:
$(893\ J/K+775\ g\times 4.184\ J/g.K ) \times(27.38-25.00)\ K=9.84\ kJ$
Negative value because it's an exothermic process.
Number of moles of $C$:
$0.300\ g\div 12.011\ g/mol=0.0250\ mol$
Enthalpy of combustion:
$-9.84\ kJ/0.0250\ mol=-394.0\ kJ/mol$
