Answer:
18.11
Explanation:
Look at the file I attached
I marked a new point E for explanation purposes.
to find out the length of AC, we need to find out the length of CD and the length of CD = length of BE.
To find out the length of BE, we need to know AE, and
AE is AD - BC
AE = 11 - 4
AE = 7
Now we have AE
Use the Pythagoras theorem to calculate BE
AE² + BE² = AB²
7² + BE² = 16²
16² - 7² = BE²
207 = BE²
√207 = BE
Since BE = CD
The length of CD is √207
Now use the Pythagoras theorem again
AD² + CD² = AC²
11² + (√207)² = AC²
121 + 207 = AC²
328 = AC²
√328 = AC
AC = 18.11