From the following data, calcualte value added by firm X and by firm Y:
(i) Closing stock of firm X 20
(ii) Closing stock of firm Y 15
(iii) Opening stock of firm Y 10
(iv) Opening stock of firm X 5
(v) Sales by firm X 300 ltbr. (vi) Purchases by firm X from firm Y 100
(vii) Purchases by firm Y from firm X 80
(viii) Sales by firm Y 250
(ix) Import of raw material by firm X 50
(x) Exports by firm Y 30