Last minute ACT math question.HELP!!!

Test Preparation
1

<p>This is from 59F
Kaylee is planning to purchase a car. She will need to borrow some of the money and has a chart, shown below, to use to approximate her monthly payment. The chart gives the approximate monthly payment per $1,000 borrowed.
Monthly payment per $1,000 borrowed for various annual rates and various numbers of payments
Number of monthly payments
Annual interest rate 36 48 60
5% $29.97 $23.03 $18.87
8% $31.34 $24.41 $20.28
10% $32.27 $25.36 $21.24
12% $33.22 $26.34 $22.24</p>

<ol>
<li>A local dealership is having an end-of-the-model-year clearance sale and is offering 5% annual interest on new-car loans for 36, 48, or 60 months. The maximum amount Kaylee can budget for her monthly car pay- ment is $300. Of the following loan amounts, which one is the maximum Kaylee can borrow at 5% annual interest and stay within her budget? A. $10,000 B. $13,000 C. $14,000 D. $15,000 E. $20,000</li>
<li>Another dealership is offering 5-year loans with a 9% annual interest rate. Kaylee uses her chart to esti- mate the payment per $1,000 borrowed. Of the fol- lowing, which is most likely the monthly payment per $1,000 borrowed? F. $20.52 G. $20.76 H. $20.85 J. $21.00 K. $21.74</li>
</ol>

2

<ol>
<li><p>You can reverse engineer questions like these, since there is no one “specific” answer - just the correct one out of the five. I’ll start with choice E - $20000 would mean $18.87 * 20 since the chart represents per $1000 borrowed. This equals to $377.4 / month, obviously out of her budget. Then you go to choice D - $15000 would mean $18.87 * 15 which equals to $283.05, which is under $300 / month.</p></li>
<li><p>A 9% interest rate is between 8% and 10%. So using that information, we can conclude that her 5-year plan (aka 60-month plan) would be of ($20.28 + 21.24) / 2, which is $20.76. Choice G</p></li>
</ol>

3

For number 43, why didn’t you multiply 18.87 by 20,000? I know that the answer will be way over if we do that, but can you explain the logic behind not adding 1000 values to the interest rates?