can someone help my answer is incorrect

You have a 15mL sample of acetylcholine (a neurotransmitter) with an unknown concentration and a pH of 7.59. You incubate his sample with the enzyme acetylcholinesterase to convert all of the acetylcholine to choline and acetic acid. The acetic acid dissociates to yield acetate and hydrogen ions. At the end of the incubation period, you measure the pH again and find that it has decreased to 6.82. Assuming there was no buffer in the assay mixture, determine the number of nanomoleyof acetylcholine in the original 15mL sample. Acetylcholine Choline Acetate acetycholine in original sample Write the Henderson-Hasselbalch equation for a propanoic acid solution (CH3CH2CO2H,pKa=4.874) Using the equation to calculate the quotient [A][HA] at three different pH values. pH=4.159[HA][A]= pH=4.874[HA][A]= pH=5.228[HA][A]=