The mass of a boat is PQ in one system and the mass of the same boat is RS in another system P and R are numerical values and Q and S are units.

Given that the mass of boat = PQ in one system

Mass of boat = RS in another system

Where P, R are numerical values, Q,S are units in the respective systems

We know any physical quantity

$\text{P}={\text{N}}_{\text{1}}{\text{U}}_{\text{1}}={\text{N}}_{\text{2}}{\text{U}}_{\text{2}}$  

Therefore here also we should get$\text{PQ}=\text{RS}$