Hi, I was wondering whether I could ask a quick question re. the use of ‘le’ in relation to ‘preguntar’?
I’ve heard (I think) ‘preguntar’ used with. and without ‘le’ during the lessons. For example, I’m fairly sure that I’ve heard both ‘necesito preguntarle a su hermana’ and ‘necesito preguntar a su hermana’. In the case of talking about someone else other than you (your mother/brother/sister) is the use of ‘le’ after ‘preguntar’ flexible and/or optional?
Questions always very welcome - we’re pleased to help, and they help others who wouldn’t be comfortable asking themselves - and sometimes they help us improve the materials… 
I could easily imagine this - the former is the more ‘correct’ version, but as is often the case with such things, it’s no surprise for it to be missing in speech… with your own usage, go with whatever comes to mind first, and you’ll find yourself adapting to whatever patterns you hear most often from the people you talk Spanish to most often…
preguntar = to ask (a question)
preguntar(le) = to ask him, to ask her, to ask you
For ex:
To ask a question = Preguntar algo / Hacer una pregunta
I have to ask you a question = Tengo que preguntarte algo / Tengo que hacerte una pregunta
In your example, more often than not you will use the “le” (Puedes preguntarle a mi hermano), though occasionally you will hear Puedes preguntar a mi hermano.
I would personally stick with the “LE” option
Diolch o galon, Gaby! 
Hey guys thanks once again for clearing this up! I had a hunch that it was something that was flexible, but it’s good to have this confirmed! Greatly enjoying the course, and looking forward to starting on No.2!
Delighted it’s going so well for you…