Find the equilibrium quantity and equilibrium price for the commodity whose supply and demand functions are given. Supply: $p=90 q \quad$ Demand: $p=-q^{2}+9,000$ The equilibrium quantity is $q=$ at price $p=\$ \square$.

Step 1 ：The equilibrium quantity and price are found where the supply and demand functions intersect. This means we need to set the two functions equal to each other and solve for q (quantity). Once we have the quantity, we can substitute it back into either the supply or demand function to find the price.

Step 2 ：Set the supply and demand functions equal to each other: \(90q = 9000 - q^2\)

Step 3 ：Solve the equation for q to find the equilibrium quantity. The solutions are q = -150 and q = 60.

Step 4 ：However, the negative solution for the quantity is not feasible in this context as quantity cannot be negative. Therefore, the equilibrium quantity is 60.

Step 5 ：Substitute q = 60 back into either the supply or demand function to find the equilibrium price. The equilibrium price is 5400.

Step 6 ：Final Answer: The equilibrium quantity is \(\boxed{60}\) at price \(p=\$ \boxed{5400}\).