Exercise 21 Page 16

To begin with, we need to figure out where the line XT is located in the diagram. Points X and T are all on the back edge of the left face of the rectangular prism (or on the left edge of the back face of the prism).

As we can see, segment XT is the back edge of the left face of the prism or the left edge of the back face of the prism. This means that the planes that intersect the line are XTQ and XTS.