Question: what is the mathematical formula for the markdown price?
Answer: With a 150% markup, the additional cost per shirt is $12 * 1.5 = $18. So the cost of the shirt after the markup is $12 + $18 = $30. A markdown of 40% decreases the price of the shirt by $30 * 0.4 = $12. So the final cost of the shirt is $30 - $12 = $18.