use the 6 and 14 and solve as you would a rectangle. if you move the little triangle to the other side of the parallelogram it becomes a rectangle and the problem is solved
both y = 1 - 3/2x and y = 1 + -3/2x are correct answers, it is just that y= 1 - 3/2x is the simpler version. Adding a negative number is the same as subtracting a positive.