Its midpoint please help

Which of the following represents the length of a diagonal of this trapezoid?

Solve the system of equations using the substitution method. {y=−3x+7x=−2y−16 enter your answers in the boxes.

Multiply and simplify. (x - 4) (x^2 – 5x – 6) i will mark brainliest if your answer is right. show how you got the answer. if your answer is correct but does not show how you got the answer you will not be marked brainliest.