Answer: The second plumber can exert 4 times more torque than the first one.
Explanation:
Torque is the cross product of force which causes rotation and the distance from the axis of rotation at which the force is applied.
τ = F × r
For the first plumber,
τ₁ = F₁ × r₁
For the second plumber,
τ₂ = F₂ × r₂ = 2 F₁ × 2 r₁ = 4 F₁ × r₁ = 4 τ₁ (∵ second plumber is twice as strong as first and second wrench is twice the length of first)
⇒τ₂ = 4 τ₁
