Please Answer ASAP.

12. Apply a mechanical force f along the x-axis of a piezoelectric crystal, such as quartz, which has dimension l in that direction. The crystal will develop a polarization po, a separation of charge along the x-axis, positive on one face and negative on the other. Applying an electric field E along the x-axis causes a mechanical deformation. Such devices are used in microphones, speakers, and pressure transducers. For such systems, the energy equation is dU = TdS+f dl+Edpo and piezoelectric Gibbs function is G=U - (TS + fl + Epo). Find a Maxwell relation to determine (@po/of T.E