I'm put at a dilemma on my project need help

see the figure below with letters to better understand the problem
step 1
Find out the length BC in the right triangle BDC
we have a 45-90-45 degrees triangle
[tex]\begin{gathered} cos(45^o)=\frac{BC}{DC}=\frac{BC}{6} \\ cos(45^o)=\frac{\sqrt{2}}{2} \end{gathered}[/tex]Find out the value of BC
[tex]\begin{gathered} \frac{BC}{6}=\frac{\sqrt{2}}{2} \\ BC=3\sqrt{2} \end{gathered}[/tex]step 2
In the right triangle ABC
[tex]\begin{gathered} sin30^o=\frac{BC}{AC} \\ \\ AC=\frac{BC}{sin30^o} \end{gathered}[/tex]we have
[tex]\begin{gathered} BC=3\sqrt{2} \\ sin30^o=\frac{1}{2} \end{gathered}[/tex]substitute
[tex]\begin{gathered} AC=\frac{3\sqrt{2}}{\frac{1}{2}}=6\sqrt{2} \\ AC=8.5\text{ m} \end{gathered}[/tex]Part B
Find out the difference
8.5-6=2.5 meters