Calc
The manager of a 100-unit apartment complex knows from experience that all units will be occupied if the rent is $600 per month. A market survey suggests that, on average, one additional unit will remain vacant for each $10 increase in rent. What rent should the manager charge to maximize revenue?
1)Let x denote the number of $10 increases in rent. Then the price is p(x) = 600 + 10x
& the number of occupied units is 100-x
2)The revenue is R(x) = (rental price per unit) × (number of units rented), which becomes
R(x) = -10x^2 + ???x + 60,000 for 0 ≤ x ≤ 100.

Need help finding ???x.

Question

Calc
The manager of a 100-unit apartment complex knows from experience that all units will be occupied if the rent is $600 per month. A market survey suggests that, on average, one additional unit will remain vacant for each $10 increase in rent. What rent should the manager charge to maximize revenue?
1)Let x denote the number of $10 increases in rent. Then the price is p(x) = 600 + 10x
& the number of occupied units is 100-x
2)The revenue is R(x) = (rental price per unit) × (number of units rented), which becomes 
R(x) = -10x^2 + ???x + 60,000 for 0 ≤ x ≤ 100.

Need help finding ???x.