Notice that the base of the pyramid is a triangle, and recall that the interior angles of a triangle add up 180 degrees, therefore:
[tex]\text{?}+55^{\circ}+70^{\circ}=180^{\circ}[/tex]
solving for ?, we get:
[tex]\begin{gathered} \text{?}=180^{\circ}-70^{\circ}-55^{\circ} \\ \text{? = 55}^{\circ} \end{gathered}[/tex]
