The drawing shows a positive point charge +q₁, a second point charge q₂ that may be positive or negative, and a spot labeled P, all on the same straight line. The distance d between the two charges is the same as the distance between q₁ and the spot P. With q₂ present, the magnitude of the net electric field at P is twice what it is when q₁ is present alone. Given that q₁ = +20.9 C, determine q₂ (in C) when it is positive.

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