Physics Question

dude was is you exam board - if your doing salter horners edexcel I'll try and get you the answers from the book if ya like?

Signals from a transmitter of 0.1m wavelength situated at a height of 2m above the ground are picked up by a receiver in a radio telescope 22m above ground at a distance of 1 km. It is desired to screen the receiver from these signals by erecting an absorbing screen 50m from the transmitter. How high must it be if the received power is to be reduced by a factor of 100? (Neglect reflections from the ground.)