My boys are 3 months old and I have been feeding them Rat and Mouse muesli from PAH. Today I have changed to Rat Rations though

I have some confusion after reading things on fb groups about how to make your mix.
I bought No 11A and Daily Rat 3 for my ratties but have read a lot of people suggest adding to the mix.
The two things I see added to the mix mainly is the HBB mix and the Seed mix. Most people work there mixes out by percentages but I am honestly rubbish at maths and this is where I am getting confused as well as working out the percentage to feed the rats.
I am also wondering how to administer the Daily Rat 3 supplement.
I have ordered 2 kg of No11 but was also wondering what amount is best to buy to last longer as the postage is quite expensive.
Any help will be massively appreciated, thank you!