Pls if a module is 20 credits and I scored 50. How do I calculate 10 credit hours from the score?

I scored 50 in a 20 credit module but i want to know how 10 credit hours will be calculated from that module because I have a higher score in another 10 credit module but I need a total of just 20. So how do you find 10 credits from the 20 credit module where I scored 50