Replace the letters in the diagram with a different number from 0 to 9, such that the sum of the four numbers on all edges are the same, and the sum of the three numbers on all three corners are the same.
D E F
G H I J
In other words, A+C+F+J = A+B+D+G = G+H+I+J and
A+B+C = D+G+H = F+I+J.
(In reply to wording change
by Cory Taylor)
As the problem stands, E is useless, for it doesn't appear in any of the sums; its only function is to use up a number.