1. **State the problem:** We want to find the perimeter of a triangle, which is the total length around the triangle. 2. **Formula:** The perimeter $P$ of a triangle is the sum of the lengths of its three sides: $$P = a + b + c$$ where $a$, $b$, and $c$ are the side lengths. 3. **Important rule:** Make sure all side lengths are in the same units before adding. 4. **Example:** Suppose the sides are $a=5.3$, $b=4.7$, and $c=6.1$ units. 5. **Calculate the sum:** $$P = 5.3 + 4.7 + 6.1 = 16.1$$ 6. **Round to 1 decimal place:** The perimeter is already at 1 decimal place, so $$P = 16.1$$ units. 7. **Summary:** Add all side lengths and round the result to 1 decimal place to find the perimeter.