For 14a through 14d, tell which expressions require you to rename mixed numbers before you can subtract. find each difference. write each expression and the difference as an equation in the correct box answer

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.

i would have to say it is c.