Question:
Find the angle whose supplement is four times its complement.
Solution:
Let the measure of the required angle be $x^{\circ}$
Then measure of its complement $=(90-x)^{\circ}$
And, measure of its supplement $=(180-x)^{\circ}$.
Therefore,
$(180-x)=4(90-x)$
$\Rightarrow 180-x=360-4 x$
$\Rightarrow 3 x=180$
$\Rightarrow x=60$
Hence, the measure of the required angle is $60^{\circ}$.