Given: ab||cd .
if the coordinates of point a are (8, 0) and the coordinates of point b are (3, 7), the y-intercept of ab ? if the coordinates of point d are (5, 5), the equation of line cd is = +

(8,0)(3,7)
slope = (7-0) /(3-8) = -7/5

y = mx + b
slope(m) = -7/5
(3,7)

7 = -7/5(3) + b
7 = -21/5 + b
7 + 21/5 = b
35/5 + 21/5 = b
56/5 = b 

y = -7/5x + 56/5 <=== the y int of AB is 56/5

y = mx + b
slope(m) = -7/5
(5,5)

5 = -7/5(5) + b
5 = - 7 + b
5 + 7 = b
12 = b

y = -7/5x + 12 <=== equation of line CD

The coordinates of point a right now is (-3,-1) you have to multiply these coordinates by a factor of 2 to get (-6,-2)