Calculate the Selling Price (SP)

Given the Cost Price ($CP = \text{₹}210$) and the required gain percentage ($90\%$), we calculate the Selling Price ($SP$) using the formula: $SP = \frac{100 + \text{Gain}\%}{100} \times CP$

$SP = \frac{100 + 90}{100} \times 210 = \frac{190}{100} \times 210 = 399$

Relate Marked Price (MP) with Selling Price (SP)

A discount of $5\%$ is offered on the Marked Price ($MP$) to arrive at the Selling Price ($SP$). The relation is given by: $SP = \frac{100 - \text{Discount}\%}{100} \times MP$

$399 = \frac{100 - 5}{100} \times MP$

Solve for Marked Price (MP)

Rearranging the equation to solve for $MP$: $MP = \frac{399 \times 100}{95}$

$MP = \frac{39900}{95} = 420$