6) FN=7.

The diagram shows a tangent FQ and a secant FPN. The lengths are FP = 3, FN = 7, and FQ = x. According to the tangent-secant theorem, FQ^2 = FP * FN. Substituting the given values, we have x^2 = 3 * 7. This simplifies to x^2 = 21. Solving for x, we get x = sqrt(21).