$[4]$ Strain Rosette was attached to the surface of the plane wing. Because of the loading on the plane wing, following strains were recorded. ${}_a=0\mathrm{.}0004,{}_b=0\mathrm{.}0002,{}_c=-0\mathrm{.}0002,$ where ${}_a$ is $$ at $=0,{}_b$ is $$ at $=60,$ and ${}_c$ is $$ at $=120.$ Obtain the maximum shear strain $(15$ point$)$ and show the plane it acts on$.(10$ point$)$