find angle sum therom

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Sum of the interior angles of any triangle is 180° .
Thus ;
[tex]y + 48° + 90° = 180°[/tex]
[tex]y + 138° = 180°[/tex]
Subtract sides 138°
[tex]y + 138° - 138° = 180° - 138° \\ [/tex]
[tex]y = 42°[/tex]
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