Решите систему неравенств:

а)[tex] \left \{ {{x\ \textgreater \ 2} \atop {x\ \textless \ 7}} ight. [/tex]

б)[tex] \left \{ {{2x\ \textgreater \ -4} \atop {x \leq -7}} ight. [/tex]

в)[tex] \left \{ {{2t-1 \geq 0} \atop {4-2t \leq 0}} ight. [/tex]