The supply at three sources is 50, 40 and 60 units respectively while the demand at the four destinations is 20,30,10 and 50 units. In solving this transportation problem
(a) a dummy source of capacity 40 units is needed
(b) a dummy destination of capacity 40 units is needed
(c) no solution exists as the problem is infeasible
(d) none solution exists as the problem is degenerate