The answer is a bit confusing, so I did some research and fount the original question. This is the complete question:
"If measurements of a gas are 75L and 300 kilopascals and then the gas is measured a second time and found to be 50L, describe what had to happen to the pressure (if temperature remained constant). Include which law supports this observation".
From that:
1) Data:
V1 = 75 liter
P1 = 300 kPa
V2 = 50 liter
P2 = x
T = constant.
2) Analysis (physical law)
Boyle's law states that the volume of a fixed amount of gas, at constant temperarature, is inversely related with the pressure.
In mathematical form that statement becomes into this equation:
PV = constant (at constant T)
=> P1V1 = P2V2.
Then, the decreasing of the volumen (compression) is accompanied by an increase of the pressure.
3) So, using Boyle's law with the data given:
300 kPa * 75 liter = x * 50 liter
=> x = 300 kPa * 75 liter / 50 liter = 450 kPa.
Answer: following Boyle's law, when the gas passed from 75 liter to 50 liter the pressure had to increase from 300 kPa to 450 kPa.