Again I'm somewhat stuck with a task. This time my while loop should return a string of comma separated numbers. I do get the comma separated numbers out when I print them but the whole thing should be inside a string, and that's where I fail.

The code I use:

```
a = 7
b = ""

while a <= 20:
    b += (str(a) + ", ")
    a = a + 3

ANSWER = b          # Same result with str(b)

```

This produce: `7, 10, 13, 16, 19,` and not `"7, 10, 13, 16, 19,"`
I don't think I should hard code it in... Any pointers on this?

Regards