4) TL=8.

The diagram shows a secant TKL and a secant TPL. The lengths are TK = 2, TL = 8, and TP = x. According to the intersecting secants theorem, TK * TL = TP * TQ (where Q is the other intersection point of the secant TPL with the circle). However, the diagram labels TP as x and does not provide a length for TQ. Assuming the secant is TPL and the external part is TP=x and the whole secant is TL=8, and the other secant is TKL with TK=2 and KL is unknown. If we assume the theorem is applied to point T, then TK * (TK + KL) = TP * (TP + PQ). Given TL=8, and assuming L is the external point and T is on the circle, this setup is unclear. If L is the external point, and LT is a secant, and LP is a secant, then LT * (part of LT) = LP * (part of LP). The diagram shows TL=8, and TK=2, and TP=x. If L is the external point, then the secant is LKT, so LK * LT = LP * (LP+PQ). This is not solvable. If T is the external point, then TK * TL = TP * (TP + PQ). We have TK=2, TL=8, TP=x. We need PQ.