When a company produces and sells x thousand units per week, its total weekly profit is P thousand dollars, where Upper P equals StartFraction 1000 x Over 100 plus x squared EndFraction . The production level at t weeks from the present is x equals 4 plus 2 t. Find the marginal profit, StartFraction dY Over dx EndFraction and the time rate of change of profit, StartFraction dP Over dt EndFraction . How fast (with respect of