At the equilibrium price p, we can solve for the quantity of goods x :
demand = supply
5200 - 0.0005x = 2800 + 0.0003x
2400 = 0.0008x
x = 3,000,000
With this quantity of goods, the equilibrium price is
p = 5200 - 0.0005 (3,000,000)
p = 5200 - 1500
p = 3700