The length of the total segment is WY = 19. We know X is on the line segment and that WX = 11. It's required to find the length of segment XY.
The total segment WY is made of the smaller segments WX and XY and it follows that:
WX + XY = WY
Substituting the known values:
11 + XY = 19
It can be found that
XY = 19 - 11 = 8
Answer: XY = 8