Chapter 3.1, Problem 38E

In $\Delta ABC$ and $\Delta DEF$, you know that $\angle A\cong \angle D$, $\angle C\cong \angle F$, and $\overline{AB}\cong \overline{DE}$. Before concluding that the triangles are congruent by ASA, you need to show that $\angle B\cong \angle E$. State the postulate or theorem that allows you to confirm this statement $\left(\angle B\cong \angle E\right)$.