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Answer:
$30
Step-by-step explanation:
Val's cost is ...
[tex](2500\text{ W})\times\dfrac{4\text{ h}}{1\text{ da}}\cdot\dfrac{1\text{ kW}}{1000\text{ W}}\cdot\dfrac{\$0.10}{1\text{ kWh}}\times30\text{ da}\\\\=\dfrac{2500\cdot4\cdot\$0.10\cdot30}{1000}=\boxed{\$30}[/tex]
It costs Val $30 a month to run her AC.