Two identical piano wires have a fundamental frequency of 600 c/s when kept under the same tension. What fractional increase in the tension of one wire will lead to the occurrence of 6 beats per second when both wires vibrate simultaneously?

Question

$$\begin {array} {1 1} (1)\;0.01 & \quad (2)\;0.02 \\ (3)\;0.03 & \quad (4)\;0.04 \end {array}$$