I have no idea how to do this question.

Answer:
PR - PQ = 18 - 4 , QR = 14
Step-by-step explanation:
If you draw the number line and put the values in you will find that RS = 4 , PS - PR
then we know that RS = PQ
PQ = 4
PR - PQ = 18 - 4 , QR = 14