Answer:
13 Units
Step-by-step explanation:
In Triangle BCD
DC=DA+AC
DC=5+11=16
Since BCD is a right triangle
BC²=BD²+DC²
20²=BD²+16²
BD²=20²-16²
BD²=144
BD²=12²
BD=12 Units
In Right Triangle BAD
AB²=BD²+AD²
=12²+5²
=144+25
=169
AB²=13²
Therefore, AB=13 Units