1. **State the problem:** Find the 19th term of the arithmetic progression (AP) 54, 51, 48, ... 2. **Formula used:** The $n$th term of an AP is given by $$a_n = a_1 + (n-1)d$$ where $a_1$ is the first term and $d$ is the common difference. 3. **Identify values:** Here, $a_1 = 54$ and the common difference $d = 51 - 54 = -3$. 4. **Calculate the 19th term:** Substitute $n=19$ into the formula: $$a_{19} = 54 + (19-1)(-3)$$ $$a_{19} = 54 + 18 \times (-3)$$ $$a_{19} = 54 - 54 = 0$$ 5. **Answer:** The 19th term of the AP is $0$.