Why the decrease in one in the power of the final answer

We calculated the force as:

$$F = 64 \times 10^{-14} \text{ N}$$

To express 64 as a number between 1 and 10, we divide it by 10:

$$64 = 6.4 \times 10^1$$

When multiplying powers with the same base, you add the exponents:

$$F = 6.4 \times 10^{(1 + (-14))} \text{ N}$$ $$F = 6.4 \times 10^{-13} \text{ N}$$

The power decreased from $-14$ to $-13$ because we increased the coefficient from 64 to 6.4 (divided by 10), so we had to compensate by multiplying by $10^1$, which effectively added 1 to the exponent.