Question

if centroid of triangle formed at x=0 and y=0 then x+y=3

Answer 1

When x=0 y=3 & when y=0 x=3
so the coordinates of the three vertices of the triangle are (0,0);(0,3);(3,0)
the formula for centroid of a triangle is (x1+x2+x3)/3 & (y1+y2+y3)/3

so the coordinates of the centroid are (3,3).