Here's how to calculate 7.0 x 10⁻³ - 8.0 x 10⁻⁴ in scientific notation and with the correct significant figures:

1. Adjust the Exponents

* To subtract numbers in scientific notation, they need to have the same exponent. Let's adjust 8.0 x 10⁻⁴:

* 8.0 x 10⁻⁴ = 0.80 x 10⁻³

2. Subtract the Coefficients

* Now we have: 7.0 x 10⁻³ - 0.80 x 10⁻³

* Subtract the coefficients: 7.0 - 0.80 = 6.2

3. Keep the Exponent

* The exponent remains the same: 6.2 x 10⁻³

4. Significant Figures

* Both original numbers have two significant figures (7.0 and 8.0).

* Our answer should also have two significant figures.

Final Answer: 6.2 x 10⁻³