Could someone please answer on both parts and tell me how I am supposed to solve this? I am heavily confused on this problem and there is no reference given by my professor.

A phone cord is 5.18 m long. The cord has a mass of 0.215 kg. A transverse wave pulse is produced by plucking one end of the taut cord. The pulse makes four trips down and back along the cord in 0.879 s. What is the tension in the cord? Answer in units of N