The extent of their liability in the firm would be X— Rs.20,000 : Y— Rs.15,000 : and Z— Rs.10,000. This is because the personal assets of each partner are subtracted from their capital balances to determine their net capital in the firm. Therefore, X's liability in the firm would be Rs.80,000 - Rs.20,000 = Rs.60,000, Y's liability would be Rs.60,000 - Rs.15,000 = Rs.45,000, and Z's liability would be Rs.40,000 - Rs.10,000 = Rs.30,000. Thus, the extent of their liability in the firm is X— Rs.20,000 : Y— Rs.15,000 : and Z— Rs.10,000.