[NTG-context] equation to right margin

I have the following which works, except for the fact that the equation number does not go to the right margin. \startplaceformula \startformula[align=middle, prefix=no] \startcases[distance=2pt] \NC \[21-(9 - n^2)\NC =□^\prime\]\NR \NC\hfill n^2+12 \NC=□^\prime.\NR[eq04] \stopcases \stopformula \stopplaceformula I expect that I have missed something pretty basic here, so any guidance will be greatly appreciated. All best, Alan