It doesn't seem that the test creator relies on your ability to differentiate between absolute and relative (or gauge) pressure. It's not mentioned anywhere, other than in B where he wants you to give the absolute pressure, which is impossible to answer, since no ambient pressure is given.
It's not really possible to give an answer at all since the described situation is not static. If the mass is increased to $150\ kg$, it will launch piston 1 rapidly in the air. Furthermore, in a static situation, the pressure below B is/must be the same as below piston A or anywhere else in the fluid. The whole question gives me the idea that the creator of the test doesn't really know what he's talking about.
I think he just wants to hear what the relative pressure in the fluid would be, if the mass on piston B is $150\ kg$, and piston A is frozen. Then you would come to
$3316\ kgf/m^2$ or $32.1\ kPa$ relative, assuming a gravitational acceleration of $9.81\ m/s^2$.
The absolute pressure doesn't matter anyway, since only relative pressure will be able to do any work. You can mention that the ambient pressure should be given to be able to give an absolute pressure, but in my experience, smartassery is rarely rewarded in school. Although the teacher is just plain wrong here and he should accept his fault...