UV and RV are secant segments that intersect at point V.

Circle C is shown. Secants U V and R V intersect at point V outside of the circle. Secant U V intersects the circle at point T, and secant R V intersects the circle at point S. The length of U V is 12, the length of T V is a, the length of R S is 5, and the length of S V is 4.

What is the length of TV?

1 unit
1Two-thirds units
2One-half units
3 units