To calculate the percent increase in the amount of interest paid between a household with a 740 credit score and one with a 730 credit score, we first need to determine the total interest paid for each credit score.
For a 740 credit score, the total interest paid is:
$$\text{Total Interest Paid}_{740} = \$20,700.00 - \$18,000.00 = \$2,700.00$$
For a 730 credit score, which falls into the next category (670-739) with an 18% interest rate, the total interest paid is:
$$\text{Total Interest Paid}_{730} = \$21,240.00 - \$18,000.00 = \$3,240.00$$
Now, we calculate the percent increase in the amount of interest paid:
$$\text{Percent Increase} = \left( \frac{\text{Total Interest Paid}_{730} - \text{Total Interest Paid}_{740}}{\text{Total Interest Paid}_{740}} \right) \times 100$$
Plugging in the values we have:
$$\text{Percent Increase} = \left( \frac{\$3,240.00 - \$2,700.00}{\$2,700.00} \right) \times 100$$
$$\text{Percent Increase} = \left( \frac{\$540.00}{\$2,700.00} \right) \times 100$$
$$\text{Percent Increase} = 0.2 \times 100$$
$$\text{Percent Increase} = 20.0\%$$
So, the correct answer is **D. 20.0%**. The percent increase in the amount of interest paid between a household with a 740 credit score and one with a 730 credit score is **20.0%**, rounded to the nearest tenth.