Relative to the $x$ axis, side AB is oriented at an angle of:

$\tan {\theta }_{AB}=\frac{240 mm}{180 mm} \therefore {\theta }_{AB}=+53.{13}^{\circ }$

Write a strain transformation for side AB:

$$\begin{gathered} +1,000 \mu \epsilon ={\epsilon }_x {\cos }^2(53.{13}^{\circ })+{\epsilon }_y {\sin }^2(53.{13}^{\circ }) \\ +{\gamma }_{xy} \sin (53.{13}^{\circ }) \cos (53.{13}^{\circ }) \end{gathered}$$