Given: (x is number of items)
Demand function: d(x)=5000.5x\displaystyle {d}{\left({x}\right)}={500}-{0.5}{x}
Supply function: s(x)=0.3x\displaystyle {s}{\left({x}\right)}={0.3}{x}

Find the equilibrium quantity:  

Find the producers surplus at the equilibrium quantity: