The four ages (Yugas) The four yugas equal one yuga-cycle (divya-yuga)
Satya-yuga: 1,728,000 years Treta-yuga: 1,296,000 years Dvapara-yuga: 864,000 years Kali-yuga: 432,000 years An age of Manu (manvantara) The life of Manu = 71.35 yuga-cycles i.e. 308,232,000 years
We are now in the 28th yuga-cycle of the current Manu, Vaivasvata.
Fourteen Manus rule in one day of Brahma
Vaivasvata is the seventh Manu in this day of Brahma.
A day of Brahma = 1000 yuga-cycles
One year of Brahma = 360,000 yuga-cycles
The life of Brahma = 36 million yuga-cycles = the life of the universe = 311,040,000,000,000 years.
Shri Ram descended almost at the end of Thretha yug... so there you go... any more q's ?
BTW these details are from Shrimad Bhagawatam - Author Vyasadev, who is also the author of 4 Vedas !