Brain teaser

I have added this one to the puzzles.

I have posted Bertie's answer but I have whited it out.  I don't want to spoil anyone's fun LOL

If you want the answer you will have to ask for it :))

Mmm,  I do not know........

It's taken a while, but, 6789 = 5.

Ok Bertie - Why is that?      You have to justify your answer or it doesn't count.  LOL  :))

I didn't want to spoil your, or someone elses, enjoyment. The answer is in a private message, publish it if you wish.

Thanks Bertie,

That looks like one convoluted answer. I shall give it closer scrutiny :)

Maybe there is more than 1 convoluted answer?

I wonder if the anon poster has an answer?    :D