i need help with a question ...
ΔPQR has vertices P(1, 3), Q(-1, 1), and R(5, 1). Determine the coordinates of the centroid of ΔABC.
What goes centroid mean and how do you solve it!
There is no such thing as "the" center of a general triangle. A triangle has many different kinds of center just as a collection of numbers has many different kinds of average. There is a very extensive online encycolpedia about triangle centers here:
ENCYCLOPEDIA OF TRIANGLE CENTERS
The formulas it gives use either trilinear or barycentric coordinates which are both quite different from ordinary Cartesian coordinates.