Just to clarify, I think its pretty unlikely you'll need to full mark the exam in order to score a 50 in French - as is the case for just about every LOTE I can think of. Like, to emphasise it even more - only 4 people got a 50 in French last year, and 199 people got an A+ for GA3. It's pretty hard to full mark everything. To even get over a study score of 35, you have to basically be fluent in the language.
If you want a more "accurate" prediction, speak to your teacher. They have the experience of having taught lots of students, all with varying scores, throughout the years.
That being said, the marks needed to get a certain study score change every year, and there are a fair few variables that can change around too.
Just to re-iterate though - focus on working hard and putting in your best possible effort - don't stress about how many marks you need in order to get x study score. Put in the effort, and it'll pay off.