Answer
$170N$
Work Step by Step
As the bracket is in equilibrium hence
$\sum \tau_{pivot}=0$
$\implies F_{sx}\times 7.2+Mg\times 9+mg\times 28=0$
This simplifies to:
$F_{sx}=-\frac{9Mg+28mg}{7.2}$
We plug in the known values to obtain:
$F_{sx}=\frac{(9\times 0.85+28\times 4.2)\times 9.8}{7.2}=-170N$
The negative sign shows that the force is in the opposite direction.
