Have to disagree with JA's claim that "tack and tack back" is limited to a T-bone situation.
IF Y tacks and a bow on bow situation results, Y must still tack back or otherwise keep clear. And, if necessary, a dial-up by R to give Y room to do so makes it all good.

Is Y required to do a tack and tack back with R?
When Y reaches her close hauled course, if she has not crossed clear ahead of R, boats will be on a course for collision between R’s bow and Y’s starboard side, with Y required to keep clear by rule 10.  In this scenario, there will not be sufficient space for Y to tack back onto starboard so as to keep clear of R, so the ‘tack and tack back’ provision of Case 101 does not apply, and the only way for boats to avoid contact is for Y to stand on, and R to give her room by bearing away and passing astern of her, thus giving Y the room to avoid R that Y is entitled to.  If Y is not keeping clear of R, she is exonerated because she is sailing within the room to which she is entitled.

For tack and tack back to work according to Case 101, the hailed boat has to be advanced on the hailing boat so that the hailing hailed boat is not pointing bow to side.