I'm having trouble with this question any ?

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.

For what values of the variable x is the expression square root of 7x+14+ square root of 7-x a real number?

Solve each quadratic equation by factoring and using the zero product property. x^2 + 18x = 9x