5.7 of anything minus 3.9 of the same thing leaves 1.8 of them.
Using simple interest, it is found that her interest charge this month will be of $30.
<h3>Simple Interest</h3>
Simple interest is used when there is a single compounding per time period.
The amount of interest after t years in is modeled by:
I(t) = Prt
In which:
- r is the interest rate, as a decimal.
In this problem, considering the time in years, the parameters are:

Hence:

Her interest charge this month will be of $30.
More can be learned about simple interest at brainly.com/question/25296782
Step-by-step explanation:
5 a = $4.45
x1.4
7 apples = $6.23
1 apple = 0.89
9.79 / 0.89 = 11
11 apples