What is the area of this polygon

What is the missing constant term in the perfect square that starts with x^2 -20x

Is each relation a function? if so, state whether it is one-to-one or many-to-one. 3. (-4,7), (-3,5), (1,4), (3,-8), (5,-11) 4. (-4,8), (-2,4), (0,1), (2,4), (4,8) 5. (-2, 1), (-2,3), (0,-3), (1,4), (3,1)

How do you use the elimination method for this question? explain, because i really want to understand!