PLZ HELP ME WITH THIS

Answer this question, only if you know the answer. 30 points and brainliest!

Quadrilateral wxyz is on a coordinate plane. segment yz is on the line x+y=7 and segment xw is on the line x+y=3. which statement proves how segments yz and xw are related

Express the following as a function of a single angle. cos(60) cos(-20) - sin(60) sin(-20)