A rigid weightless platform $\textbf{PQRS}$ shown in the figure ( not drawn to the scale) can slide freely in the vertical direction. The platform is held in position by the weightless member $\textbf{OJ}$ and four weightless, frictionless rollers. Points $\textbf{O}$ and $\textbf{J}$ are pin connections. A block of $90\:kN$ rests on the platform as shown in the figure
The magnitude of horizontal component of the reaction ( in $kN$) at pin $\textbf{O}$, is
- $90$
- $120$
- $150$
- $180$