Your team is writing a fancy new text editor and you've been tasked with implementing the line numbering.
Write a function which takes a list of strings and returns each line prepended by the correct number.
The numbering starts at 1. The format is `n: string`. Notice the colon and space in between.
**Examples:**
```python
number([]) # => []
number(["a", "b", "c"]) # => ["1: a", "2: b", "3: c"]
```
def number(lines):
    n = 0
    l = []
    for i in lines:
        n += 1
        l.append(str(n) +': '+ i)
    return l
def number(lines):
    n = 0
    l = []
    for i in lines:
        n += 1
        l.append(str(n) +': '+ i)
    return l