Let's assume
It started in 2000
so, t=0 in 2000
we can use formula
we can plug value
In 2005, the same survey was made and the total amount of gamma ray bursts was 7.3 million
so, at t=2005-2000=5
P(t)=7.3 million
we can plug value and then we can solve for r
now, we can plug back
now, we have
P(t)=1 billion =1000 million
so, we can set it and then we can solve for t
approximately
Year is 2000+192
year is 2192................Answer