sodium sesqui carbonate is a double salt of sodium carbonate and sod bicarbonate -> Na2CO3.NaHCO3
with phenolthalein,
Na2CO3.NaHCO3 -----changes to-------------->> NaHCO3.NaHCO3
N FACTOR =1
x= 40 ml
with meth orange,
Na2CO3.NaHCO3 -----changes to-------------->> 3 H2CO3
N FACTOR =3
y =120 ml
so i think ans shud be 80 ml.