In the J-tube above, Y and X are on the same horizontal level and 30cm³ of air is trapped above Y when the atmospheric pressure is 75cm Hg, calculate the volume of air trapped above Y when 15cm Hg is now poured into the limb above X

• A.15 cm³
• B.25 cm³
• C.35 cm³
• D.45 cm³
• E.