The correct answer is 6.62x10-9.
To simplify this expression, we need to first understand the rules of scientific notation. In scientific notation, a number is written in the form a x 10^b, where a is a number between 1 and 10, and b is an integer (positive, negative, or zero).
To simplify this expression, we need to first convert the numbers 28 and 69 to scientific notation. We do this by moving the decimal point so that the number is between 1 and 10, and then multiplying or dividing by a power of 10 to make the number have the same value as before. For example, we can convert 28 to scientific notation by moving the decimal point two places to the left, resulting in 2.8, and then multiplying by 100 to compensate for the decimal point movement, resulting in 2.8 x 10^2. Similarly, we can convert 69 to scientific notation by moving the decimal point one place to the left, resulting in 6.9, and then multiplying by 10 to compensate for the decimal point movement, resulting in 6.9 x 10^1.
With the numbers in scientific notation, we can now simplify the expression. To do this, we need to remember the rules of exponents. In particular, when multiplying numbers with the same base, we add the exponents, and when dividing numbers with the same base, we subtract the exponents. In this case, we have two numbers with the same base (10) and we are dividing them, so we subtract the exponents. This gives us:
(28 x 102) - (69 x 101)
= 2.8 x 10^2 - 6.9 x 10^1
= 2.8 x 10^1 - 6.9 x 10^0
= 28 x 10^1 - 6.9 x 10^0
= 28 x 10^0 - 6.9 x 10^-1
= 28 x 1 - 6.9 x 0.1
= 28 - 0.69
= 27.31
We can now convert this result to scientific notation. To do this, we move the decimal point so that the number is between 1 and 10, and then multiply or divide by a power of 10 to make the number have the same value as before. In this case, we can move the decimal point two places to the right, resulting in 0.0273, and then multiplying by 100 to compensate for the decimal point movement, resulting in 2.73 x 10^-2. However, since the exponent is negative, this means the number is very small, so we can simplify it further by moving the decimal point one more place to the right, resulting in 0.00273, and then multiplying by 10 to compensate for the decimal point movement, resulting in 2.73 x 10^-3. However, since the exponent is still negative, this means the number is even smaller, so we can simplify it further by moving the decimal point one more place to the right, resulting in 0.000273, and then multiplying by 10 to compensate for the decimal point movement, resulting in 2.73 x 10^-4. Since the exponent is now a multiple of 3 (which is a common factor of 10), we can simplify it further by dividing the exponent by 3, resulting in 2.73 x 10^-4 / 3 = 0.9 x 10^-4. Finally, we can move the decimal point one more place to the right, resulting in 0.09 x 10^-4, and then multiplying by 10 to compensate for the decimal point movement, resulting in 9 x 10^-5. This is the final result, which is in scientific notation