On target A's vector calculator, put one leg of the dividers on Te and the other on R.
Te towards R represents our own ship's course and speed. The vector calculator rule is Te never moves so if we intend to turn to starboard R must move to the right.
Pivot on Te and "swing" R to the right until it touches the NRML. Label that position as Rc.
At this point, our own ship is not changing speed so make sure the distance from Te to R is the same as Te to Rc.