1. The problem is to find the sum of the first 3 terms of an arithmetic progression (AP). 2. The formula for the sum of the first $n$ terms of an AP is: $$S_n = \frac{n}{2} \times (2a + (n-1)d)$$ where $a$ is the first term, $d$ is the common difference, and $n$ is the number of terms. 3. For $n=3$, the sum of the first 3 terms is: $$S_3 = \frac{3}{2} \times (2a + 2d) = \frac{3}{2} \times 2(a + d) = 3(a + d)$$ 4. This means to find the sum of the first 3 terms, you add the first term and the common difference, then multiply by 3. 5. Example: If $a=5$ and $d=2$, then $$S_3 = 3(5 + 2) = 3 \times 7 = 21$$ 6. So the sum of the first 3 terms is 21. This is a typical SS3 question on arithmetic progression sums.