Answer:
750$
Step-by-step explanation:
lets say the increase is x times 10$. it means manager asks for (500+10x) and earns it from (100-x) apartments. Revenue will be the product of the two:
[tex](500 + 10x)(100 - x) = 50 \: 000 - 500x + 1 \: 000x - 10 {x}^{2} = 50000 + 500x - 10 {x}^{2} [/tex]
its a parabola, and its maximum is on the vertex, or at
[tex]x = - \frac{b}{2a} = - \frac{500}{ - 20} = 25[/tex]
so he should add 10$ 25 times, or ask 750$