>31. The normalized wave functions $\Psi_1$ and $\Psi_2$ correspond to the ground state and the first excited states of a particle in a potential. The operators $\hat{A}$ act on the wave function as:
$$\hat{A}\Psi_1=\Psi_2\text{ and }\hat{A}\Psi_2=\Psi_1$$
The expectation value of the operator $\hat{A}$ for the state $\hat{A}=(3\Psi_1+4\Psi_2)/5$ is:  
(A)  0  
(B) -0.32  
(C)  0.75  
(D)  0.96




Not able to understand how to determine expectation value when ground state and first excited states are given.