the answer
X'Y' and XY are parallels, measX'Y'T = measXYT, there is similarity between the two triangles, we can find YT by using theorem of thales,
it is TY' / TY =TX' / TX =X'Y' /XY, so TY' / TY = TX' / TX = 9/ TY =6/ 2+6=6/8
and then 9/ TY = 6/8 therefore TY= 12