You can solve this problem by applying the "Intersecting chords theorem". You must follow the proccedure below:
1. Let's represent each lenght, as below:
(P will be the point of intersection)
AP=4 cm
CP=6 cm
DP=3 cm
BP=n
2. Therefore, you have:
APxCP=BPxDP
APxCP=nxDP
3. Now, you must clear "n", as below:
n=APxCP/DP
4. When you substitute each value into n=APxCP/DP, you obtain:
n=(4 cm)(6 cm)/3 cm
n=24 cm²/3 cm
5. Finally, the result is:
n=8 cm
