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put this solution on YOUR website! .
The pulling force (same as the tension of the rope) is the force, which
provides acceleration of the sled at 1.5 m/s^2.
According to the Newton's second law, the value of this force (its magnitude) is
F = ma = 11 * 1.5 = 16.5 newtons. ANSWER
Solved.
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The given mass of the boy (42 kg) is an excessive info, irrelevant to the problem.