For reference: In an acute triangle ABC, H is the orthocenter and O is the circumcenter. Find the $ \measuredangle OBH, if ~\measuredangle A - \measuredangle C=24^o $
My progresss: I made the drawing and the following relationships
$\measuredangle AOC = 2(\alpha +\theta)\\
\triangle AOB ~and ~\triangle BOC~and \triangle AOC~are ~isosceles\\
\measuredangle DAO = 90^o -(\alpha+\theta)\implies \measuredangle ABE = \theta\\
\measuredangle DAB=90-\theta $

Your diagram already shows it: $\angle OBH$ is the red angle;
$$\angle OBH = \alpha - \theta$$
And from the given,
$$\alpha - \theta = \angle A - \angle C = 24^\circ$$