Find the sum of the sequence 7, 77, 777, 7777, . . . to n terms.

Explanation

To find the sum of the sequence 7, 77, 777, 7777, ..., up to n terms, we can follow these steps:

### Step 1: Identify the pattern of the sequence
The sequence can be expressed as:
- 1st term: 7
- 2nd term: 77 = 7 * 11
- 3rd term: 777 = 7 * 111
- 4th term: 7777 = 7 * 1111
...