Aldehydes, Ketones and Carboxylic Acids

Complete reaction of acetaldehyde with excess formaldehyde, upon heating with conc. NaOH solution, gives P and Q . Compound P does not give Tollens' test, whereas Q on acidification gives positive Tollens' test. Treatment of P with excesscyclohexanone in the presence of catalytic amount of p -toluenesulfonic acid (PTSA) gives product R .
Sum of the number of methylene groups (−CH2−) and oxygen atoms in R is _______.