Rosa has a company that makes chairs. If they sell chairs, they will be priced at (60-0.3n) dollars each, how many chairs must be sold to have a income of $1080? You must take into account that n≤40.

Solution:
1. Given:
- Price per chair: (60 - 0.3n) USD
- Income: 1080 USD

2. Set up the equation for income:
n \times (60 - 0.3n) = 1080

3. Expand the equation:
60n - 0.3n^2 = 1080

4. Rearrange to form a quadratic equation:
-0.3n^2 + 60n - 1080 = 0

5. Multiply through by -10 to simplify:
3n^2 - 600n + 10800 = 0

6. Use the quadratic formula n = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} with a = 3, b = -600, and c = 10800:
n = \frac{600 \pm \sqrt{(-600)^2 - 4 \cdot 3 \cdot 10800}}{2 \cdot 3}
n = \frac{600 \pm \sqrt{360000 - 129600}}{6}
n = \frac{600 \pm \sqrt{230400}}{6}
n = \frac{600 \pm 480}{6}

7. Solve for n:
- First solution: n = \frac{600 + 480}{6} = \frac{1080}{6} = 180
- Second solution: n = \frac{600 - 480}{6} = \frac{120}{6} = 20

8. Considering the constraint n \leq 40, only n = 20 is valid.

Thus, Rosa needs to sell:
n = 20 chairs to get an income of 1080 USD.