Estimate the the values of tissue , S , and P for a tissue that neither gains nor loses weight when equilibrated

Estimate the the values of  Ψ_tissue, Ψ_S, and Ψ_P for a tissue that neither gains nor loses weight when equilibrated with a 0.4 molal mannitol solution and in which, when placed in a 0.6 molal mannitol solution, 50% of the cells are plasmolyzed?

Ψ of 0.4 molal mannitol = -1 MPa

Ψ of 0.6 molal mannitol = -1.5 MPa