고체역학 (Gere) — Analysis of Stress and Strain: Problem 7.2-26

7.2-26 A rectangular plate of dimensions 125 mm $\times$ 75 mm is subjected to tensile stress $\sigma_x = 67 \text{ kPa}$ and compressive stress $\sigma_y$. If it is known that the normal stress along the diagonal $t-t$ is $\sigma_t = -6.57 \text{ kPa}$, find stress $\sigma_y$ on element A.