It's not about the amount you right. So long as you include something to support your answer form the source (it could even be the date it was written), and link it into what you already know about waht it is saying then you shoud be fine.
Like maddie says its not the amount it's the evaluation and showing of knowledge that gets marks. Also use a clear structure in your answers and it will keep you on the right track,
For example for the "what does source a tell you about ... in ...?
To answer this use the structure of: source a shows me that ... , also it shows me ...
These type of question is only for two marks so don't spend too long on it, and if you can't find a second point then use own knowledge on the situation.
Hope that helps.