Country A and country B are two neighboring countries. The inverse supply and demand functions for electricity (TWh) in these two countries are given by:

Sa = 7,5+0.15Xa
Da = 21 -0.075Xa
Sb = 15+0.15Xb
Db = 24 -0.0375Xb

where Sa, is supply price in country A, Da is demand price in country A and Xa, is the corresponding volume in country A. Similar notation for country B. These functions are only valid in the ranges where both prices and quantities are non- negative. Outside these ranges prices and quantities are defined as zero.

b) What is the equilibrium price and corresponding total production when there is one common market and no constraint on transmission?