x + y = 138
x - y = 88
--------------------------
x + y = 138
-x
y = -x + 138
--------------------------
-> substitute " -x + 138" into y
x- (-x+138) = 88
x + x - 138 = 88
2x - 138 = 88
+ 138
2x = 226
2x/2 = 226/2
x= 113
---------------------------
-> substitute "113" into x to get y
113 - y = 88
-113 -113
-y= -25
y = 25
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Our final answers are the two numbers "113" and "25"