The point T is in the line SU, which means that it is between the points S and U. Therefore, the distance ST + TU must be equal to the distance between S and U. We know the distance between S and T and the distance between T and U, therefore:

Applying the data provided by the problem:

We now need to find the distance between T and U, which is given by the following expression:

Applying the data from x we calculated:

The numerical length of the line TU is 5.