Answer:
15.33cm
Step-by-step explanation:
when you try to draw out this figure, satisfying the fact that Ad and Ac are both straight lines. you find the ultimately it forms a right-angled triangle with sides AC and AD and hypotenuse CD.
Now, you may use Pythagoras theorem to solve:
AC^2 + AD^2 = CD^2
12.3^2 + 9.15^2 = CD^2
CD^2 = 235.0125
CD = square root of 235.0125 = 15.33cm
Hope this helps
