Margin vs Markup: the 5-minute lesson
Margin is profit as a share of price; markup is profit as a share of cost. A "50% markup" on a $40 cost = $20 profit = $60 price = only 33% margin. Sellers who price by markup while thinking in margins routinely undercharge 10–30%. Ecommerce rule of thumb after fees & shipping: aim for 50%+ gross margin or ads will eat you alive.
Pure arithmetic — no estimates needed.