Question:
Find the angle which is four times its complement.
Solution:
Let the measure of the required angle be $x$.
Then, measure of its complement $=\left(90^{\circ}-x\right)$.
Therefore,
$x=\left(90^{\circ}-x\right) 4$
$\Rightarrow x=360^{\circ}-4 x$
$\Rightarrow 5 x=360^{\circ}$
$\Rightarrow x=72^{\circ}$
Hence, the measure of the required angle is $72^{\circ}$.