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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

1. $90$
2. $120$
3. $150$
4. $180$
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