What is the ph of the plasma

At 37C, if the plasma pH is 7.4 and the plasma concentration of HCO3 is 15 mM, what is the plasma concentration of H2CO3? What is the plasma concentration of dissolved CO2? If metabolic activity changes the plasma concentration of dissolved carbon dioxide to 3 mM and HCO3 remains at 15mM, what is the pH of the plasma?