One of the angles forming a linear pair is an obtuse angle. What kind of angle is the other?

Given one of the angles of a linear pair is obtuse, then the other angle should be acute because only then their sum will be 180^o.
 

For example, let two angles are angle a and angle b.
let angle a = 108^o ..(obtuse angle) , angle b = x

So, for two angles forming a linear, the sum of the angles should be 180^o.

$\begin{array}{c}\mathrm{i}.\mathrm{e}. \angle \mathrm{a} + \angle \mathrm{b} = {180}^{\mathrm{o}}\\ \to 108° + \mathrm{x} = 180°\\ \to \mathrm{x} = 72° .. (\mathrm{acute} \mathrm{angle})\end{array}$