The range of rejected bags is found by summing and subtracting the 400 grams to 2.1 grams, because the second one represent the acceptable margin.
So, we have:
However, this interval represents the accepted range. The rejected range would be the opposite. Therefore, the asked range is:
Step C is incorrect: When you simplify exponents the rules are: for adding or subtracting, the base and the exponent must be equal; when multiplying the base must be the same, and the exponents will add; when dividing the base must be the same and the exponent will subtract.
Step D is incorrect: The last division is wrong, you could treat it with the general rule of exponents, subtracting the exponents of the base 10.
The correct procedure of each step is:
x------> the number
we know that
% is equal to
By using proportion
divide by both sides
the answer is