I honestly just need some advice So...

Ok I original live in the U. S Florida but my patents are UK citizens and you know trump and all that but anyways we had to move to the UK and in Florida I was in 8th grade in middle school and school had just started so I just started the 8th grade I wasn't in school long enough to make a month anyways I moved to UK and got put in year 9 and I now have a big science test coming up that's suppose to sum up year 7 year 8 and year 9 work and school in Florida is super easy compared to school here anyways I have 13 days to study for the test and I'm trying to but I can't memorize all the stuff and I was wondering if any of you have some tips and tricks to help me study or if you recommend any studying apps I would really appreciate it I'm literally in my room about to cry because I'm so tried and stressed out pls help me

The kidney filters potentially toxic substances in the blood, and thus “clears” the blood of those substances. this clearance function is dependent upon and proportional to the diffusion gradient of the substance across filtering capillaries, i.e. if the concentration of the substance is doubled, twice as much will be cleared from each ml of blood that is filtered. suppose that the body produces a constant amount of a substance x per unit of time. the kidneys eliminate substance x at a rate directly proportional to the concentration of the substance and the volume of blood cleared each minute (c): elimination = c × [x], where [x] is the steady-state concentration of substance x. imagine an individual with an initial concentration of x equal to [x]0 who develops kidney disease. her baseline clearance c0 drops to one half of the original (½c0). what is the new steady state concentration of x? (for simplicity, assume that substance x is 100% filtered by the kidney).