x + y = 58 -----equation 1
x - y = 20 -----equation 2
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Add equations 1 and 2
x + y = 58
+ x - y = 20
2x = 78
x = 39
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Substitute x=39 to equation 1
x + y = 58
y = 58 - x
y = 58 - 39
y = 19
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Therefore the ordered pair is (39,19).
