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There are, roughly, pi times 10 million seconds in a year (the actual number is 31,556,926, but "pi times 10 million" is close and easier to remember). So just multiply that by that large number of years, and there's your answer. So 1,000,000,000 years equals 3.1556926 × 1016 seconds.
There are 1263141040 seconds in 40 years
10 years = 315,569,260 seconds.
18 years is about 568,036,800 seconds.
About 1,009,843,200 seconds in 32 years.
20 years = 631,138,519 seconds.
25 years = 788,923,149 seconds.
10 years = 315,569,260 seconds.
70 years is about 2,209,032,000 seconds.
800,000,000,000 seconds = 25,351.0117 years.
13 years = 410,240,038 seconds.
74 years is about 2,335,262,400 seconds.