How is the number $8.104 \times 10^7$ correctly read aloud?

Eight point one four times ten to the seventh.

Eight point one zero four times ten to the seventh.

Eight point one zero four times ten to the seven.

Eight hundred fourteen times ten to the fourth.

Which is the most precise and standard way to read the number $1.5 \times 10^9$ in a scientific context?

One and a half times ten to the ninth.

One point five times ten to the ninth.

Fifteen times ten to the eighth.

One point five times ten raised to nine.