The formula used for determining gas pressure, volume and temperature interaction would be PV=nRT. 
<span>•	What is the temperature in Kelvins?
</span>You already right at this part. Kelvin temperature formula from celsius should be:
K= C+273.15= 
<span>K= 27 +273.15 = 300.15 
It is important to remember that the formula in this question is using Kelvin unit at temperature, not Celcius or Fahrenheit.
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<span>•	Assuming that everything else remains constant, what will happen to the pressure if the temperature decreases to -15 ºC?
</span>In this case, the temperature is decreased from 27C into -15C and you asked the change in the pressure. 
Using PV=nRT formula, you can derive that the temperature will be directly related to pressure. If the temperature decreased, the pressure will be decreased too. 
<span> If you increase the number of moles to 6 moles, increase temperature to 400K and reduce the volume to 25 L, what will the new pressure be?
</span>PV=nRT
P= nRT/V
P= 6 moles* <span>0.0821 L*atm/(mol*K) * 400K/25L= 7.8816 atm</span>
        
             
        
        
        
Advantages 
less wasted energy 
Reduces fossilisation
Disadvantages 
- Expensive 
- doesn't look nice ( apparently) 
        
             
        
        
        
It is definitely not A. B is an effect. I would say C because D is more of a conservative answer , C is more of a liberal answer, and we currently live in a liberally swayed world. They are probably looking for C. It is not in your nature to be bad.