plz assist, i need help

A spaceship traveled from Earth to Sirius, the brightest star in our night sky. According to the computers on the spaceship, the spaceship traveled a distance of 6.9 lightyears and the journey took 11.5 years. Assume that the Earth and Sirius are stationary with respect to one another and ignore any effects of acceleration. (Hint: A lightyear is the distance traveled by light in one y which is just c multiplied by one year, or 9.46 x 10"3 km. In many problems it is simpler to le year, since c often cancels out.) a) How fast did the spaceship travel? (3) b) What was the duration of the journey according to the people on Earth? (4) c) How far away is Sirius from Earth according to the people on Earth? (3) d) During the journey, the spaceship sends mission updates back to Earth. The receivers on Earth are set to receive signals at 400 MHz. At what frequency should the spaceship send the signals so that the messages will be received on EHHHY