Suppose two firms (Firm 1 and Firm 2) are competing against each other in a duopoly market. Suppose further that the market demand is given by the equation P=700−30(q₁​+q₂​), where P is the price of the product and q₁​ and q₂​ are the quantities produced by Firm 1 and Firm 2 respectively. If both firms have constant marginal costs of $20, what is the Cournot equilibrium quantity produced by each firm?
A. 15 units
B. 20 units
C. 25 units
D. 30 units