I’ve already answered Part A. Part B & C have the same drop down answers choices.

Given
[tex]\begin{gathered} \tan (12)=\frac{x}{6} \\ \tan (78)=\frac{6}{x} \end{gathered}[/tex]To check whether the value of x is found using both equation:
It is known that,
[tex]\tan \theta=\frac{oppositeside}{\text{adjacent side}}[/tex]From the given figure, it is clear that the angles of the triangle ABC,
[tex]\begin{gathered} \angle A=90,\angle C=12 \\ \angle B=180-(\angle A+\angle C) \\ =180-(90+12) \\ =78 \end{gathered}[/tex]Therefore for the angle C=12 degree,
The equation can be written as,
[tex]\tan \theta=\frac{x}{6}[/tex]Since x is the opposite side and 6 is the adjacent side.
However for angle B. the opposite side will be 6 and the adjacent side will be x.
Thus, we get
[tex]\tan \theta=\frac{6}{x}[/tex]Hence, Andre and Mia both are correct.