The third term of an A.P. is 7 and the seventh term exceeds three times the third term by 2. Find the first term, the common difference and the sum of first 20 terms.

Explanation

To solve the problem step by step, we will use the properties of Arithmetic Progressions (A.P.).

### Step 1: Define the terms of the A.P.
Let the first term of the A.P. be \( a \) and the common difference be \( d \).

### Step 2: Write the expressions for the 3rd and 7th terms.
The \( n \)-th term of an A.P. can be expressed as:
\[
...