Two firms operate in a single good market and produce quantities (q₁) and (q₂) respectively. They face the market demand curve (P = 12 - Q). If Firm 1 has zero fixed costs and variable costs equal to $1 per unit, what is the profit-maximizing quantity (q₁) for Firm 1?

a) (q₁ = 3)
b) (q₁ = 4)
c) (q₁ = 5)
d) (q₁ = 6)