Question:
A quadrilateral has three acute angles, each measuring 75°. Find the measure of the fourth angle.
Solution:
Sum of the four angles of a quadrilateral is $360^{\circ}$.
If the unknown angle is $x^{\circ}$, then:
$75+75+75+x=360$
$x=360-225=135$
The fourth angle measures $135^{\circ}$.