The point (x, y) = (-8, 4) is in the 2nd quadrant
Above the x-axis (because the y value is positive)
To the left of the y-axis (because the x value is negative).
I am not kidding: do a quick drawing.
Therefore, the angle P (which is measured from the x-axis, going countercloswise --- up and to the left) will be between pi/2 (90 deg.) and pi (180 deg.).
Angles are [almost]** always measured from the x-axis, going counterclockwise.
When you draw the line to the origin (0, 0), also think of the vertical portions: The vertical side going straight down to the x axis (measuring 4 units in length, because y = +4), and the horizontal side measuring 8 in length (because x = -8).
The hypotenuse of this triangle is the line from A to origin, and its length is found by using the Pythagorean theorem.
hypotenuse = sqrt(64 + 16)
Sine (P) = y/hypotenuse = 4 / sqrt(80)
Cosine (P) = x/hypotenuse = -8 / sqrt (80) (yes, the cosine is negative in the 2nd quadrant)
Tan = sin/cos = 4/-8 = -0.5
You can use any of these ratios to find the value of angle P (remembering that the value must be in the 2nd quadrant)
P = arctan(-0.5) = 180 - 26.565 = 153.435 degrees