The fundamental frequency (in hertz) of a piano string is directly proportional to the square root of

Question:

The fundamental frequency (in hertz) of a piano string is directly proportional to the square root of its tension and inversely proportional to its length and the square root of its mass density. A string has a frequency of 100 hertz. Find the frequency of a string with each property.
(a) Four times the tension
(b) Twice the length
(c) Four times the tension and twice the length