How do plants absorb light energy from sun

Curious carl calculated the density of a cube to be 4.50 g/cm3. what is the density of the cube in g/l?

Agas contained within a piston-cylinder assembly undergoes three processes in series: process 12: compression with pv= constant from 1 bar and 1 liter to 4 bar. process 23: constant pressure expansion to 1 liter. process 31: constant volume calculate the pressure and volume at each state, and sketch the processes on a p-vdiagram labeled with pressure and volume values at each numbered stat

What’s #16 asking me and how do i solve it?