In a labour market with inelastic supply and elastic demand, the expressions of demand and supply are given by:

QS = 500

QD = 800 - 5 wD

With supply defined in terms of working hours per day, and w being the total cost of 1 working hour/day for companies.

a) Determine the incidence of a 20% tax on wages.

b) If the supply function is no longer completely inelastic and is defined by, analyse the incidence in this new situation and compare it with that of the previous paragraph.