Step-by-step explanation:
3 x^3-15x^2+18x 3(x^3-5x^2+6x)
Sin angle that equals the 1/2 value is the 30 degree on the 1st Quadrant.
The angle of 30 degree on the 3rd Quadrant is equivalent to (formula and circle in the 1st photo) 180 + 30 = 210°.
So theta = 210° (3rd Quadrant) = 30° (1st Quadrant).

Now just transfer the cos 30° to the 3rd Quadrant and the signal will be negative (as shown in the 2nd photo attached).
Lower extreme- 8
Lower quartile- 20
Median- 30
Upper quartile- 35
Upper extreme- 42
Hope this helps!