Adepartment buys 300 shirts at a cost of $1,800 and sells them for $10 each. find the percent markup rounded to the nearest percent

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

5   1/4   miles per hour

step-by-step explanation:

15   3/4 / 3 = 5   1/4