On a day in Winter in Mathsland the temperature (°C) of all the major cities was recorded.

The results are as follows:

Mathsburg is at -9°C,

Pythagorasville is at -49°C, Eulerville is at -29°C,

Newtown is at -19°C and Fishwick is at 11°C.

What is the temperature difference between the warmest and coldest city?