These are my final quiz questions basically the ones i didnt understand I need to get these right please please please help

Plz heeeeeeelp plz give me the answer

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.

Complete the solution of the equation. find the value of y when x equals to 28 x+3y=28