So start with your standard numbers. Divide 1.6 by 4 and you get 0.4
With the exponents, since you’re dividing, you keep the base and subtract the exponents. So 3-6=-3
You’d get 0.4 x 10 to the -3 but that’s not correct scientific notation because you have to have a value 1 or larger.
Move the decimal to the right one place (making the standard number larger) and make the exponent smaller to balance it out.
4 x 10 to the -4 power.
