Explanation:
let d+e=2 be equation 1
let d-e=4 be equation 2
lets make d the subject in equa 1
d = 2-e equation 3
put equation 3 in 2
2-e=4
e=2-4
e=-2
put e=-2 in equa 1
d-2=2
d=4
e is -2 and d is 4
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