why can we know this....
1. the 5th trumpet gives us a 150 day value which if we understand encompasses the 6th trumpet as well we see the 6th trumpet is 75 days. thus the multiple of the trumpets is +75. so trumpet 1 starts with 450.
2. we see tis in dan 7.
12 As concerning the rest of the beasts, they had their dominion taken away: yet their lives were prolonged for a season and time.
season and time = 360+90 = 450. so at the start of the trumpets the 4th beast is in power