There have been about two years before the birth of Christ for every 3 years of history in all. If 4,000 years passed before Christ's birth, what is the total number of years in history?

Question

(Years BC)/(Years AD + Years BC) = 2/3
4000 y = (2/3)(Years AD + Years BC)
6000 y = (Years AD + Years BC)
= Total history

Could you please explain that further? I don't understand.

So... 4,00 yrs is B.C. and 4,00 must be 2/3 of total history, so total history is 6,000 years? Did I do that right?

I meant "4,000 yrs is B.C. and 4,000 must be 2/3 of total history"