jquery APR loan slider calculator incorrect and needs resetting

I have a website with a jquery slider that you use to slide to the amount you wish to borrow over 28 days, it then shows you instantly the amount you would expect to pay back, this calculation is dependant upon the apr (the interest payable) on the amount you borrrow, at the moment the apr is incorrect, it should be set at (i think) 391.1% per year, all loans are repayed in 28 days, so this calculation would be as follows , you borrow £225, the apr is 391.1% per year so the amount you would pay back in 28 days would be £292.50, at the moment it is calculating the payback amount at £281.25 instead of £292.50 so the calculator is set incorrectly and I don't know how to change it so it calculates correctly so need a freelancer with jquery experience to be able to set the correct apr so the slider calculates the correct payback amounts. The website is [login to view URL] and the slider is on the home page, if you slide the slider to borrow £225 you will see that it calculates you will pay back £281.25 when it should state £282.50, I don't know which file to change this setting in so whoever could do the initial change for me then let me know which file I should change in future incase of another apr change that would be great (I looked in all the .js files but cannot figure out how to do it lol), I have attached a screenshot that may help, thanks for looking at my small project.