A mathematician says something is wrong with the shading on this graph. What do you think it is?

When we have a black dot in some value, means that the value is included in the set of solutions (associated with the signs ≤ ≥, and with solid lines)

When we have a white dot, means that the value is outside the set of solutions (associated with the signs < > and with dashed lines).

In this case, we can see the solid line across the solid point, but the dashed line does not cross over the white dot, this implies that the white dot belongs to the set of solutions (because is inside the shaded area) so this is an incongruence.

The dashed line should pass over the white dot.

answer: she must produce at least 9,000 windows in order to make a profit of $48,000

explanation:

48,000 - 12,000 = 36,000

36,000/4 = 9,000