If $\psi$ _P = 0 $\psi$ _S = -0

If $\psi$ _P = 0.3 MPa and $\psi$ _S = -0.45 MPa, the resulting $\psi$ is

A) +0.75 MPa.
B) -0.75 MPa.
C) -0.15 MPa.
D) +0.15 MPa.
E) -0.42 MPa.