A.
If the chemical composition is different, even if they carry the same UN number, the PSN May be different. For example, with a PSN showing a star symbol, the technical name shown in parenthesis could be different. From a chemical viewpoint, those are not the same chemical substance. The Dangerous Goods Regulation, however, is a rule governing the transportation of dangerous goods. If the UN number is the same, the packing group is the same, and the physical condition is the same, the same Packing Instruction will apply for shipping. As it says in the third bullet point in DGR 5.0.2.11 subparagraph (h), ?gthose with the same UN number, packing group and physical state?ii.e. solid or liquid?j, provided they are the only dangerous goods in the package and the total net quantity does not exceed the maximum net quantity shown in the List of Dangerous Goods?h you do not need the take those in account in the calculation of the?gQ?hvalue. The Dec aration is to be written as follows:

UN 1993 Flammable liquid, n.o.s. (xxxxxxxxx)	Cl. 3	PG III	20L	PI 355
UN 1993 Flammable liquid, n.o.s..(yyyyyyyyy)	Cl. 3	PG III	10L	PI 355
UN 1993 Flammable liquid, n.o.s. (zzzzzzzzzz)	Cl. 3	PG III	30L	PI 355
		All packed in one
		Fibreboard box

Since the maximum allowable net quantity of UN 1993 PG III PI 355 is 60L, there is no need for a ?gQ?h calculation, and therefore, no need to enter the ?gQ?h value.