Calculate the Discount Amount

Subtract the selling price from the marked price to find the total discount given in rupees: $\text{Discount} = 1200 - 840 = 360$

$\text{Discount} = 1200 - 840 = 360$

Relate Discount to Percentage x

Since the discount of $x\%$ is given on the marked price, set up the percentage equation: $x\% \text{ of } 1200 = 360$

$\frac{x}{100} \times 1200 = 360$

Solve for x

Isolate $x$ by dividing 360 by 12 and simplifying: $x = \frac{360}{12} = 30$

$x = \frac{360 \times 100}{1200} = 30$