(A) The supply function generally is considered to have positive slope. Qa has positive slope. Qb has negative slope, so is probably the demand function.
supply function: Qa
demand function: Qb
(B) The equilibrium price is the price that makes supply equal to demand.
Qa = Qb
50 +p = 200 -4p
5p = 150
p = 30
The equilibrium price is 30.
(C) The price elasticity of supply is computed as
Es = (dQa/dp)·(P/Qa) = 1·p/(50+p)
Es = p/(50+p)
At p=30, the numerical value is Es = 30/80 = 3/8. Qualitatively, the supply is inelastic.
