Quadratic equations help

Segment xz is bisected by point y. if xy = 12x, and the measure of xz = 18x – 6, solve for x

Mrs. gehrke said cheddar weighs 16.8 pounds. he actually weighs 15.2 pounds. what is the percent error?

Parabolas y=−2x^2 and y=2x^2 +k intersect at points a and b that are in the third and the fourth quadrants respectively. find k if length of the segment ab is 5.