Answer:
[tex]12\sqrt[]{2}[/tex]
Explanation:
The sketch of the situation is given below
We need to find length B.
Now Pythagoras's theorem gives
[tex]B^2+(4\sqrt[]{7})^2=20^2[/tex]
which simplifies to
[tex]B^2+112=400[/tex]
subtracting 112 from both sides gives
[tex]B^2=400-112[/tex][tex]B^2=288[/tex]
Taking the square root of both sides gives
[tex]B=\sqrt[]{288}[/tex]
[tex]\boxed{B=12\sqrt[]{2}\text{.}}[/tex]
which is our answer!
