5.0 lb.

Explanation

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

\(R_{r} d_{r}=R_{b} d_{b}\)

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.Solving for Rb, our missing value, and plugging in our variables yields:

\(R_{b}=\frac{R_{d} d_{a}}{d_{b}}=\frac{30 \mathrm{lb} \times \times 1 \mathrm{ft.}}{6 f \mathrm{ft} .}=\frac{30 \mathrm{ft} . \mathrm{lb} .}{6 \mathrm{ft} .}=5.0 \mathrm{lb}\)

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