Profit Calculation:
To calculate the selling price of the pen, let's first determine the cost price and profit percentage.

Step 1: Cost Price (CP) Calculation:
Given that the pen is sold for Rs 19.15, and the profit percentage ranges from 30% to 40%, we can assume that the cost price is the minimum value that generates a 30% profit.

Let's assume the cost price of the pen is 'x.'

Profit = Selling Price - Cost Price
Profit = Rs 19.15 - x

According to the given condition, the profit percentage is between 30% and 40%. So, we can write the equation as:

Profit Percentage = (Profit / Cost Price) * 100
30% = (Profit / x) * 100

Solving the equation:
30/100 = (19.15 - x) / x
0.3 = (19.15 - x) / x
0.3x = 19.15 - x
1.3x = 19.15
x = 19.15 / 1.3
x = 14.73

Therefore, the cost price (CP) of the pen is Rs 14.73.

Step 2: Profit Calculation:
We need to find the profit percentage when we sell the pen at the cost price of Rs 14.73.

Profit = Selling Price - Cost Price
Profit = Selling Price - Rs 14.73

Profit Percentage = (Profit / Cost Price) * 100
40% = (Selling Price - 14.73) / 14.73

Solving the equation:
40/100 = (Selling Price - 14.73) / 14.73
0.4 = (Selling Price - 14.73) / 14.73
0.4 * 14.73 = Selling Price - 14.73
5.892 = Selling Price - 14.73
Selling Price = 14.73 + 5.892
Selling Price = Rs 20.622

Therefore, the selling price of the pen is Rs 20.622.

Summary:
- The cost price (CP) of the pen is Rs 14.73.
- The selling price of the pen is Rs 20.622.