Question

Find center of mass in equilateral triangle if it's side a and masses is 4

Answer 1

the center of mass of an equilateral triangle (or any triangle) is independent of it's mass.

The centre of mass of an equilateral triangle will always be the centroid of a triangle.

If the equilateral triangle is ABC, and you produce an angular-bisector/perpendicular (it'll be the same line) from point-A to line-BC, then the center of mass  will be the point on this line 2a/3 from point A.