Oh honey, that's a big number! Technically, you read it as "four quintillion." But let's be real, you'll probably just say "four followed by a whole lotta zeros" when you see it. Keep on counting those zeros, you're doing great!
Four sextillion
The number 4,000,000,000 is read four billion.
They're simply used for clarity - to make the number easier to read.
9116
To write 0.81 in words, you would say "zero point eight one." The number before the decimal point is read as a whole number, followed by "point," and then the numbers after the decimal point are read individually. In this case, "8" is read as "eight" and "1" is read as "one."