We developed a simple model for a flare loop, which was used to fit the emission in the microwave (17GHz) and millimetre-wave (80GHz) ranges for the giant flare of 1991 June 4. The simplicity of the model enabled the exploration of a wide range of parameters in a reasonable time. It was possible, using the simple model, to derive from the 17- and 80-GHz data the magnetic field and the number density for every measurement point in the time range we chose to fit.