Answer
$78.4^{\circ}$
Work Step by Step
r= d/2 =$ \frac{10.4\,cm}{2}=5.20\,cm$
h= 25.3 cm
Let $\theta$ be the angle the side of the cone make with the base.
Then, $\tan \theta =\frac{opposite\,side}{adjacent\,side}=\frac{h}{r}=\frac{25.3}{5.20}=4.86$
$\theta=\tan^{-1}(4.86)=78.4^{\circ}$
