As can be seen from the figure, P A = 8/ 1 = 8g/cm 3, P B = 2/2 = 1g/cm 3.
Because A and B have the same mass, their volume ratio is V A: V B =p B: P A = 1:8.
Their side length ratio is L A: L B = 1:2, and their area ratio is S A: S B = 1:4.
The same mass means the same gravity, so the pressure on the horizontal plane is the same.
So the ratio of their pressures is PA: PB = (f/SA): (f/SB) = SB: SA = 4:1.
So you should choose B.
I hope it helps you!