1. **State the problem:** We are given the formula for simple interest: $$I = Prt$$ where $I$ is the interest earned, $P$ is the principal, $r$ is the interest rate, and $t$ is the time in years. 2. **Goal:** Solve for $P$ in terms of $I$, $r$, and $t$. 3. **Formula used:** The original formula is $$I = Prt$$. 4. **Isolate $P$:** To solve for $P$, divide both sides of the equation by $rt$: $$P = \frac{I}{rt}$$ 5. **Show cancellation step:** $$P = \frac{I}{\cancel{r}\cancel{t}} \times \frac{\cancel{1}}{\cancel{r}\cancel{t}}$$ (This step shows dividing both sides by $rt$ to isolate $P$.) 6. **Final answer:** $$\boxed{P = \frac{I}{rt}}$$ This means the principal $P$ is equal to the interest $I$ divided by the product of the rate $r$ and time $t$. This formula is useful to find the original amount invested when you know the interest earned, the rate, and the time period.