Can someone explain this to me? I'm not entirely sure this question has enough information to be solved. Thanks!

Question 1
[tex]DC=AC-AD=20-16=4[/tex]
Question 2
By the geometric mean theorem,
[tex]BD^2 = (4)(16)=64 \\ \\
BD=8[/tex]
Question 3
By the Pythagorean theorem,
[tex]AB^2 = 8^2 + 16^2 \\ \\ AB^2 = 320 \\ \\ AB=8\sqrt{5}[/tex]
Question 4
By the Pythagorean theorem,
[tex]BC^2 = 8^2 +4^2 \\ \\ BC^2 = 80 \\ \\ BC=4\sqrt{5}[/tex]