Suppose your school is selling magazines subscriptions each subscription cost $20 the company pays the school half of the total sales in dollars he school must also pay a one time fee for $18 that can be sold to earn a profit of $200

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.