The coordinates of the centre of mass of the system shown in the figures are :

(1.33L, 0.167L) (0, 0) (0.33L, 1.67L) (L, L)

(1.33L, 0.167L)

Sum of masses = m + m + m + 3m = 6m x-coordinate : (m x 0 + m x L + m x L + m x 2L)/6m = 1.33L y-coordinate : (m x 0 + m x L + m x 0 + m x 0)/6m = 0.167L.