Final answer:
To calculate the annual interest rate of Kachina Caron's investment, we use the simple interest formula and rearrange it to solve for the annual rate, considering that the time period is 9 months.
Step-by-step explanation:
The correct answer is option annual interest rate.
To find the annual interest rate when Kachina Caron earned $81 from a $1800 investment in 9 months, you need to use the simple interest formula, which is I = PRT, where I is the interest earned, P is the principal amount, R is the annual interest rate, and T is time in years.
In this problem, I = $81, P = $1800, and T = 9/12 years (since 9 months is three-fourths of a year). First, we'll rearrange the formula to solve for R:
R = I / (PT)
Substituting the given values:
R = $81 / ($1800 × (9/12))
R = $81 / $1350
R = 0.06
Since R is expressed as a decimal, we need to convert it into a percentage:
R = 0.06 × 100
R = 6%
The resulting annual interest rate from the investment of $1800 with an interest of $81 in 9 months is 6%.
Therefore, the annual interest rate is 6%.