Answer:
18.1 cm
Explanation:
Consider a segment parallel to CD and passing through B.
This segment will form a right-angle triangle with A
It's length would be equal to the length of CD (the missing length)
Height of that triangle:
11 - 4 = 7
CD² = 16² - 7²
CD² = 207
CD = sqrt(207)
AC² = AD² + CD²
AC² = 11² + 207
AC² = 328
AC = 2sqrt(82)
Which is roughly 18.1 cm