Can someone help me do this proof, which I am doing as practice for an upcoming test?

Beth took out a $20,000 loan for college she is borrowing money from two banks. bank a charges an interest rate of 8.5% bank b charges and interest rate of 10.5% after one year alice owes $1860 in interest how much money did she borrow from bank a

On a string instrument, the length of a string varies inversely as the frequency of its vibrations. an 11-inch string has a frequency of 400 cylces per second. find the frequency of a 10-icnch string.

Alex measured the length of an item to be 3.7 cm. the actual length is 3.5 cm. what is alex’s percent error?