Astrid,

There are instructions for writing a number in Scientific notation in the answer Sara gave to a previous question. Following her instructions the first two non-zero digits in 3,700,000,000 are 3 and 7 so put the decimal between them

3.7

To move the decimal from being between the 3 and 7 to the position of the decimal in 3,700,000,000. you need to move it 9 places to the right, in other words you have to multiply by 1,000,000,000 which is 10⁹. Thus

3,700,000,000 = 3.7 × 10⁹.

For your second problem which is to evaluate (2.5 x 10^5) (1.56 x 10^-3) write

(2.5 x 10⁵) (1.56 x 10^-3)
= (2.5 x 10⁵) × (1.56 x 10^-3)
= 2.5 × 1.56 × 10⁵ × 10^-3

Can you complete the problem now?

Penny