All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.
Using GC, there is no solutions found. Thus, planes p, q, r have no common intersection at all. They form a triangular prism since none of the planes are parallel to each other.
This question is rather straight-forward. Students should be able to interpret the results from the graphing calculator. Better students should be able to comment that it is a triangular prism.