To solve this question, follow the steps below.
Step 01: Write the numbers to have the same powers.
To do it, choose one number to transform.
Let's choose the number with the greaters power (10⁻³).
To write it with the power -4, multiply 7.94 by 10:
[tex]\begin{gathered} 7.94\times10^{-3}=7.94\operatorname{\times}10*10^{-4} \\ =79.4\operatorname{\times}10^{-4} \end{gathered}[/tex]Step 02: Solve the subtraction.
To solve the subtraction, subtract the decimals.
[tex]\begin{gathered} 79.4\operatorname{\times}10^{-4}-6.69\operatorname{\times}10^{-4} \\ =(79.4-6.69)\operatorname{\times}10^{-4} \\ =72.71\operatorname{\times}10^{-4} \end{gathered}[/tex]Step 03: Rewrite the number in scientific notation.
For a number in scientic notation a x 10ᵇ, 1 ≤ |a| < 10.
Then, divide 72.71 by 10 and multiply the exponent part by 10.
[tex]\begin{gathered} \frac{72.71}{10}\times10^{-4}\times10 \\ 7.271\times10^{-4+1} \\ 7.271\times10^{-3} \end{gathered}[/tex]Answer:
[tex]7.271\cdot10^{-3}[/tex]