The basic idea is that multiplying by 10 just moves the decimal point one place to the right. It makes the number bigger.
Examples:
3.1 x 10 = 31
3.1 x 10 x 10 = 31 x 10 = 310
Each time you multiply by another 10, the decimal point moves one more place.
In your exercise, [tex]10^3[/tex] says you're going to multiply by 10 three times in a row. So that will move the decimal point 3 places to the right.
So what do you get if you move the decimal in 4.25 three places to the right?
