The image shows an equation where the student must fill in a missing part to complete the calculation. Here’s what I can gather:

1. Equation structure: $\left( -6.4 \times 10^5 \, \frac{N}{C^2 \cdot m^2} \right) \cdot \boxed{\text{Missing Part}} = \frac{?}{mC^2 \cdot m^2}$

2. Goal: The student needs to figure out the correct multiplier to fill the empty box (missing part) to complete the unit conversion.

3. Clues and analysis:

   • The first term is $-6.4 \times 10^5 \, \frac{N}{C^2 \cdot m^2}$, involving Newtons per squared Coulomb per squared meter.
   • The result on the right side must yield some kind of expression involving $mC^2 \cdot m^2$ in the denominator.

4. What could the missing part be?
   The options visible in the interface (such as $\mu$, exponents, and $x 10^n$) suggest that:

   • The missing part likely needs to contain some power of $10$ and possibly a prefix such as micro ($\mu$).
   • You might also need a scaling factor to adjust the numerical magnitude appropriately.

Could you clarify further if this problem relates to Coulomb's law or some specific unit transformation? That context would help ensure an accurate answer.

Would you like detailed steps to solve for the correct multiplier?
Here are five questions you might find helpful:

1. How are units of Newtons, Coulombs, and meters related?
2. What is the significance of the $10^5$ factor in this equation?
3. Could the missing part involve micro units ($\mu$) or a scientific notation factor?
4. Are you trying to transform or simplify a unit conversion problem?
5. Is the goal here to match units between the terms on both sides?