Answer: The percent markup is 50%.
Explanation:
So first you divide 1800 by 300 to find out how much each shirt costs, which is $4 each. Then you subtract 10 by 4 which is 6. And finally find the percent from 4 to 6, which you can do by converting a percent like 25 into a decimal and adding 1, so 1.25. Then you multiply 4 by 1.25 which is 5, so that doesn't work. Then 1.50 * 4 which gives you 6!