Plane HKP and plane RKP are two distinct planes. Name the intersection of plane HKP and plane RKP.

They wanted you to name the line, not just mention that it is a line. In fact, it is the line KP

Apologies for the misunderstanding. The intersection of plane HKP and plane RKP is named line KP.

The intersection of two distinct planes, plane HKP and plane RKP, will be a line.

The intersection of plane HKP and plane RKP is a line.