In this diagram, we are given the following information:

• $AB \parallel CD$,
• $\angle ADB = 80^\circ$,
• $\angle CAD = 20^\circ$,
• $AC = BD$, a geometric equality.

We need to find $\angle ADC$.

Approach:

1. Parallel Lines and Transversals: Since $AB \parallel CD$, the angles created by the transversal (e.g., $\angle CAD$) will help us apply angle rules related to parallel lines.

2. **