Ross (he was on break) pours water at 6.0 c into a container with a pressure of 23. torr. he then boils the water to a temperature of 34 c. the volume changes to 18. ml and pressure to 78. torr. what was the initial volume of the water?

For this question, since the parameters volume, pressure and temperature changes, we can use the combined gas law equation.
It states that PV/T = constant 
Therefore,

Where parameters for the first instance are given on the left side and parameters for the second instance are given on the right side of the equation
Temperature in K - T1 = 6 °C + 273 = 279 K
                               T2 = 34 °C + 273 = 307 K
substituting the values in the equation

V = 55.5 mL

Combustion is the act or process of burning. therefore, i believe the answer is  a: burning wood. 

Qrepresents joules in the formula