Answer :

Shravani83
Let the 1st, 2nd, 3rd & 4th angles be a° , b° , c° & d° respectively.

a° = 54°
b° = 116°
c° = 85°
d° = ?

We know the sum of all angles of a quadrilateral is 360°.
According to the problem,
a° + b° + c° + d° = 360°
54° + 116° + 85° + d° = 360°
255° + d° = 360°
d° = 360° - 255°
d° = 105°
Therefore, the measure of the Fourth angle is 105°.
So sum of angles of quadrilateral is 360°

so let the unknown angel be x 

so the other angles are 54° , 116° , 85°

so we have 54° + 116° + 85° + x = 360° 

⇒x  = 360° - 255°

⇒x = 105°

so the fourth angle is 105°

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