Since center of dilation is the origin, this is easy. Just divide all of the x and y coordinate values by 3. Place the new point on the graph, and draw the triangle.
R' = R(3,6)/3 = (3/3,6/3)=(1,2). So R'(1,2) S' = S(-3,6)/3 = (-3/3,6/3)=(-1,2). So S'(-1,2) T' = T(-6,-6)/3 = (-6/3,-6/3)=(-2,-2). So T'(-2,-2)
So you now know the location of the 3 new points. R' at (1,2), S' at (-1,2) and T' at (-2,-2). Simply draw those 3 points on your graph and connect the lines to make a new triangle.