You are holding a pencil of mass m and length l at rest horizontally. Your thumb is pushing the right end of the pencil downward, and your index finger is pushing the pencil upward at a distance d from the right end. Assume that the pencil has uniform mass distribution. What is the magnitude of the force exerted by your thumb on the pencil?

a) mgl/2d
b) 2mgd/l
c) 2mgd/l
d) mgd/l
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