Let `C =x`. Then, `A = (x - 20)` and `B = (x - 40)`. `:. x + x - 20 + x - 40 = 120` or `x = 60`. `A : B : C = 40 : 20 : 60` `= 2 : 1 : 3`. `B's` share `= Rs. (120 xx 1/6)` `= Rs. 20`.