Aright triangle whose base is 30 units is divided into two parts by a line drawn parallel to the base. it is given that the resulting right trapezoid has an area larger by 7; 0 d 420 than the upper triangle, and that the difference between the height y of the upper triangle and the height z of the trapezoid is 20. if x is the length of the upper base of the trapezoid, these statements lead to the relations 1 2 z(x c 30) d 1 2 xy c 420, y