Question 1089540
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You have two equations:

(1)   D = S - 13.
(2)   D + S = 75.


Substitute (1) into (2). You will get

(S-13) + S = 75  ====>  2S = 75 + 13 = 88  ====>  S = {{{88/2}}} = 44.


<U>Answer</U>. Sydney is 44 years old.
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