Asample of oxygen gas has a volume of 150.0 ml when its pressure is 0.947 atm. what will the volume of the gas be at a pressure of 0.987 atm if the temperature remains constant?

Boyle's law gives the relationship between pressure and volume of gas. It states that for a fixed amount of gas at constant temperature, pressure is inversely proportional to volume of gas. 
PV = k
where P - pressure, V - volume and k - constant 
P1V1 = P2V2 
where parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation.
substituting the values in the equation
0.947 atm x 150.0 mL = 0.987 atm x V
V = 144 mL
therefore new volume is 144 mL