Instina paid interest charges of 169.05 on a 4830 invoice that was two months overdue What monthly rate of simple interest was she charged? (Do not round Intermediate calculations and round your final answer to 2 decimal places) Monthly rate month

## Step 1: Calculate the total interest for two months.<br />### The problem states that Instina paid an interest of $169.05 for two months. This is the total interest for the two-month period.<br /><br />## Step 2: Calculate the interest for one month.<br />### Since the interest is simple interest, the interest for one month is half the interest for two months. So, the interest for one month is $\$\frac{169.05}{2} = \$84.525$.<br /><br />## Step 3: Calculate the monthly interest rate.<br />### We use the simple interest formula: $I = Prt$, where $I$ is the interest, $P$ is the principal, $r$ is the interest rate, and $t$ is the time in years. Here, we want to find the monthly interest rate, so we set $t = \frac{1}{12}$ (since one month is $\frac{1}{12}$ of a year). We have $I = \$84.525$, $P = \$4830$, and $t = \frac{1}{12}$. We solve for $r$:<br />$r = \frac{I}{Pt} = \frac{84.525}{4830 \cdot \frac{1}{12}} = \frac{84.525 \cdot 12}{4830} = \frac{1014.3}{4830} \approx 0.21$.<br />Converting this to a percentage, we get $0.21 \times 100 = 21\%$.