Let CP be the original cost price of the article.
Selling price of the article at 25% profit = 1.25CP
ATQ
Gain % = 30 = (1.25 CP - 10.5 - 0.8 CP)x100/ 0.8 CP
30 = 156.25 - 1312.5/CP - 100
1312.5/CP = 56.25 - 30 = 26.25
The original cost price of the article CP = 50