Given that BC = 8 and BD = 20
Now using both values we have to find the value of CD.
We need to figure out any relation between BC and BD that can be used to find CD.
We see that common letter in BC and BD is B
so that means B must be in the middle letters C and D
C <----8---> B <-----20------> D
According to diagram we can write:
CD = BC + BD
Now plug the given values:
CD = 8 + 20
CD = 28
Hence final answer is CD = 28.