Answer:
use the formula of centroid that is
= x1+x2+x3/3
You first separate the triangle from the rectangle. Then multiply one side be one side.
To find the magnitude of a vector, take the components, square them, then add them, then take the square root. This is very similar to the Pythagorean Theorem.
For your particular problem, I’ve included a picture showing how that specific calculation is done. :)
-4(9)(-5) = (-36)(-5) because -4(9) = -36. (-36)(-5) = 180