Below is the graph of a trigonometric function. It has a minimum point at \( \left(\frac{2 \pi}{3},-8.2\right) \) and an amplitude of 5.4 . What is the midline equation of the function?

Step 1 ：\( y = A \sin\left(B\left(x-P\right)\right) + Q \)

Step 2 ：\( -8.2 = A \sin\left(B\left(\frac{2 \pi}{3}-P\right)\right) + Q \)

Step 3 ：Q = -8.2 \pm A

Step 4 ：Q = -8.2 \pm 5.4

Step 5 ：Q = -2.8