Hi all

I have a situation where I attempted to correlate the difference between mean pre and post exam scores to study time in a sample of around 60 students:

I quickly realised that that does not work so I am thinking of ways around it. I think one potential way is to convert the mean difference between pre and post, and study time to z-scores and then correlate them with each other.

Can I just ask, is that a valid line of action and if not could anyone suggest an alternative? I've been on Google all day