Answer
$ 78\ N$
Work Step by Step
Let tension at the top of cord be $T_2$.
For $m_1$ and $m_2 $, apply newton second law of motion so that;
$(m_1+m_2)g - T_2 = (m_1+m_2) a$
Since $a=0$;
$T_2 = (m_1+m_2)g$
$T_2 = (3.5\ kg +4.5\ kg) (9.8\ m/s^2)$
$T_2 = 78.4\ N$
