If  ${{dy} \over {dx}} + {3 \over {{{\cos }^2}x}}y = {1 \over {{{\cos }^2}x}},\,\,x \in \left( {{{ - \pi } \over 3},{\pi \over 3}} \right)$  and  $y\left( {{\pi \over 4}} \right) = {4 \over 3},$  then  $y\left( { - {\pi \over 4}} \right)$   equals -