The sum of the first n terms of an AP whose first term is `8` and the common difference is `20` is equal to the sum of first `2n` terms of another AP whose first term is `-30` and the common difference is `8`. Find `n`.

Explanation

To solve the problem, we need to find the value of \( n \) such that the sum of the first \( n \) terms of the first arithmetic progression (AP) is equal to the sum of the first \( 2n \) terms of the second AP.

### Step-by-Step Solution:

1. **Identify the first AP:**
- First term \( a_1 = 8 \)
- Common difference \( d_1 = 20 \)

...