Third row:
The balance stays the same as the previous row ($337.52).
We have 12 days between 9/7 and 9/18, so we can calculate the product/sum as:
[tex]S=12\cdot337.52=4050.24[/tex]
NOTE: the product/sum will be used to calculate the average balance for the month.
Fifth row:
The balance stays the same as the previous row ($399.78).
We have 11 days between 9/20 and 9/30.
Then, the product/sum is:
[tex]S=399.78\cdot11=4397.58[/tex]
Total:
The total product/sum is:
[tex]S_{\text{Total}}=1937.60+337.52+4050.24+399.78+4397.58=11122.72[/tex]
Average daily balance:
We can take the total product/sum and divide by the total amount of days.
[tex]\text{average daily balance}=\frac{11122.72}{30}=370.76[/tex]
Finance charge:
[tex]\text{ finance charge}=\frac{1.25}{100}\cdot370.76=4.63[/tex]
New balance:
[tex]\begin{gathered} \text{New balance = previous balance - payment/credits + finance charge + new purchases} \\ \text{New balance = }387.52-50+4.63+62.26=404.41 \end{gathered}[/tex]
The new balance is $404.41.
