GATE 2026 Question 59: Costs of production

Suppose that Ritwick owns two plants, Plant $X$ and Plant $Y$. Both plants produce the same industrial good. The marginal cost to produce at Plant $X$ is $4+2Q_X$; where, $Q_X$ is the quantity produced in Plant $X$, and the marginal cost to produce at Plant $Y$ is $40+Q_Y$; where, $Q_Y$ is the total quantity produced in Plant $Y$. If Ritwick plans to produce 15 units of this good, the amount of the good produced in Plant $Y$ is ______ (in integer)