Selling price per unit = Rs. 60
Total Cost Price of production = Rs. 100
Total profit = Rs. 500
Total Selling Price = Total CP + Total profit = Rs. ( 500 + 100 ) = Rs. 600
Now, Number of units sold = Total SP / (SP of one unit ) = 600 / 60 = 10 units
Now total cost increased by 30%
So, the new Total CP becomes 100 + 30% of 100 = Rs. 130
Now, I considered profit level as two possible meanings - same profit % or same total profit amount
Case (i) - Same profit percentage -
Old profit percent = $\frac{500}{ 100}$ * 100 = 500 %
New Total CP = Rs. 130
profit = 500 % of 130 =Rs. 650
Total price (SP) = Rs. (130 + 650) = Rs. 780
percentage increase in price = $\frac{New SP - Old SP}{ Old SP} * 100$
= $\frac{780 - 600}{ 600} * 100$
= 30 %
Case(ii) - If I consider same profit amount -
Total CP(new) = Rs. 130
Total profit = Rs. 500
New Total SP = Rs. 630
%age increase in price(SP) = $\frac{New SP - Old SP}{ Old SP} * 100$
= $\frac{630 - 600}{ 600 } * 100$
= 5 %