1. **State the problem:** We need to find the principal amount $P$ given the simple interest $I=18$, the rate $r=6\%$, and the time $t=3$ months. 2. **Formula:** The simple interest formula is $$I = Prt$$ where - $I$ is the interest earned, - $P$ is the principal amount, - $r$ is the annual interest rate (in decimal), - $t$ is the time in years. 3. **Convert given values:** Since $r=6\% = 0.06$ and $t=3$ months, convert $t$ to years: $$t = \frac{3}{12} = 0.25 \text{ years}$$ 4. **Substitute known values into the formula:** $$18 = P \times 0.06 \times 0.25$$ 5. **Simplify the right side:** $$18 = P \times 0.015$$ 6. **Solve for $P$ by dividing both sides by 0.015:** $$P = \frac{18}{0.015}$$ 7. **Show cancellation:** $$P = \frac{\cancel{18}}{\cancel{0.015}} \times \frac{1}{1} = 1200$$ 8. **Final answer:** $$\boxed{1200}$$ The principal amount $P$ is 1200.