Hi!
x - 36
x - 36 = y
x + y = 104
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x + x - 36 = 104
2x - 36 = 104
2x - 36 + 36 = 104 + 36
2x = 140
2x/2 = 140/2
x = 70
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70 + y = 104
70 - 70 + y = 104 - 70
y = 34
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Hope this helps! :)
-Peredhel