Question:
The three angles of a quadrilateral are 76°, 54° and 108°. Find the measure of the fourth angle.
Solution:
Sum of all the four angles of a quadrilateral is 360°.
Let the unknown angle be $x^{\circ}$.
$76+54+108+x=360$
$238+x=360$
$x=122$
The fourth angle measures 122°.