Correct Answer - Option 3 : 300

**Given:**

Cost price of article = Rs. x

Mark up percentage = 100%

Selling price = Rs. 420

Discount percentage = 30%

**Concept used:**

MP × (100 - d)% = SP

**Calculation:**

Marked price = CP + CP × 100% = 2CP

Marked price = 2x

2x × (100 - 30)% = 420

2x × 70% = 420

x = 210 × 100/70 = Rs. 300

**∴ The value of x is Rs. 300.**