Answer:
The solution is (3, -1)
Explanation:
Add the two equations together and you get ...
2d = 6
d = 3 . . . . . divide by 2
Substitute that value into either equation. For the first, that substitution looks like ...
3 + e = 2
e = -1 . . . . . subtract 3
The solution is (d, e) = (3, -1).
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Comment on the general solution
As you can see, the larger of the two solutions to this "sum and difference" problem is d=(2+4)/2, the average of the sum and difference. This is generically true for all "sum and difference" problems.