Help with mathematics

Hello can you me find all the products

Dakota earned $7.50 in interest in account a and $18.75 in interest in account b after 15 months. if the simple interest rate is 4% for account a and 5% for account b, which account has the greater principal? explain. to make it a little easier, there is an image. good luck!

How many and of which kind of roots does the equation f(x)=x3−x2−x+1