Old COALPORT Equestrian Plates

[PianoMom]

I am trying to help a friend put a value on a set of 4 Coalport Kingsware plates she inherited. They are marked England, AD1750, and the fronts show four different equestrian scenes. The titles of the plates are

• Asking the Way
  [li]At the Crossroads
  [li]Post Boys
  [li]Springing 'Em
  

If you have any information that could help me at all, I'd appreciate it. She is wondering whether these four comprise the complete set, where she might be able to sell them, and their approximate value.  Thank you for your expertise!