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The problem is based off a passage. The passage along with the answer choices are uploaded.

With a full carriage, the second ride suffers a power outage with the mechanical arm perpendicular to the horizontal. How much torque must the mechanical arm provide in order to prevent the passengers from swinging down? (Assume the mechanical arm itself does not require any torque support.)

The mechanical arm has a length of 5 m and a full carriage has a mass of 600 kg (300 kg cart plus 300 kg so I thought the answer should be 600(10)(5). They say that the answer should be 120,000 N m.

The book explains that that the mechanical arm must provide enough torque to cancel out the torque produced by the gravitational force. Hence, τ = rfsinθ = mgr = 600(10)(20).

Where did the the 20 come from?

With a full carriage, the second ride suffers a power outage with the mechanical arm perpendicular to the horizontal. How much torque must the mechanical arm provide in order to prevent the passengers from swinging down? (Assume the mechanical arm itself does not require any torque support.)

The mechanical arm has a length of 5 m and a full carriage has a mass of 600 kg (300 kg cart plus 300 kg so I thought the answer should be 600(10)(5). They say that the answer should be 120,000 N m.

The book explains that that the mechanical arm must provide enough torque to cancel out the torque produced by the gravitational force. Hence, τ = rfsinθ = mgr = 600(10)(20).

Where did the the 20 come from?