As a GEMCAR customer, you have access to GEMUNIVERSITY with all recorded GEMINAR including the one on how calculate selling price based on a cost using a margin. You would also have access to the industry standard margin based of different categories .

What is the growth margin
The gross margin is the profit calculated on the selling price of an article.
For example, for a repair shop :
 with 1 million in sales,
 with a $100 000 in profit,
We would all say that he as a 10% gross margin!
Margin Formula for a shop : Profit / Sales 
OR
Margin Formula for a product: (SellingCost) / Selling 
To calculate the selling price based on the cost with a margin in % ;
Selling price = Cost / (1Margin) 
Ex:
If an item as a cost of $100 with a margin of 40%, we should sell it for $166.67
Selling = 100 / (1  0.4) = $166.67
Margin = (166.67100) / 166.67 = 40%
At the end of the day using a margin vs a markup makes more money in your bank account.
Ex : a part at $100 sold for $100 x 140% = $140
Margin = ($140$100) / $140 = 29%
At the end of the day using a margin vs a markup makes more money in your bank account.
Ex : a part at $100 sold for $100 x 140% = $140
Margin = ($140$100) / $140 = 29%
To calculate the selling price based on the cost with a markup ;
Selling price = Cost * (1 + markup) 
Ex:
If an item as a cost of $100 with a markup of 40%, we should sell it for $140
Selling = 100 x (1 + 0.4) = $140