Subtract 13 3/4 from 71 1/4 and
divide the difference by 3 5/6.

15

Step-by-step explanation:

First, subtract 71 1/4-13 3/4, which is 57 1/2. Then, divide it by 3 5/6. The answer is 15

last option

step-by-step explanation:

given that δdef is right and isoceles,

assuming that side df is the hypotenuse means that de an ef are the other 2 sides that intersect at 90° and are of equal length.

because they are of equal length, we can say that they are congruent

because they intersect at 90°, their slopes must be opposite reciprocals.

only the last option satisfies these conditions.