A furnace produces a stack gas that has an analysis of 8.93% CO2, 1.56% CO, 0.34% SO2, 9.87% O2 and the rest N2. The coal burnt contains 1.7% N, 15% ash, and 5.5% S. While the refuse contains uncoked coal with 20.71% HV lost. 

Calculate: 

(a) Complete ultimate analysis of coal;

(b) Complete analysis of the refuse if it contains 37.93% ash; 

(c) % excess air. Establish basis as 100 kg of coal.