Answer:
Let the Dulcina's collection be 'x'
Let the Tremaine collection be 'x-39'
x + x - 39 =129
2x = 129 +39
2x = 168
x = 168/2
x = 84
Dulcina's collection = x = 84
Tremaine's collection = x - 39 = 84 - 39 = 45
in parallelogram EFGH
the mid point of diagonal EG is
(-3-5)/2,(1+5)/2=(-4,3)
similarly the midpoint of diagonal FH is
(0-2)/2,(2+6)/2=(-1,4)