Pearl Puzzles

Put the digits 1-3 (later 1-4 and 1-5) once each in the white circles and once each in the shaded circles. When 3 circles are adjacent in a straight line, the middle circle should contain the difference of the numbers in the other two circles. Some of the circles are already filled for you.

A.   B.   C.   D.  

E.   F.   G.   H.  

I.   J.   K.   L.  

M.   N.   O.   P.  

Q.   R.   S.  

The answers are here.