How Much Butane is Present as a Liquid?

hey

Butane (C4H10) has a heat of vaporization of 22.44 kJ/mol and a normal boiling point of -0.4°C. A 260-mL sealed flask contains 0.58 g of butane at -23°C. How much butane is present as a liquid in grams?

 

Any and all help would be appreciated, this problem is hard!!

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