Calculate value-added by firms A and B from the following data:
(i) Purchases by firm B from firm A 40
) Sales by firm B 80
(iii) Imports by firm B 10
(iv) Plat paid by firm B 5
(v) Opening stock of firm B 15
(vi) Closing stock of firm B 20
(vii) Purchases by firm A from firm B 20
(viii) Closing stock of firm A 20
(ix) Opening stock of firm A 10