What is the value of y when line m is parallel to line m?

a: 70
b: 110
c: 140
d: 140

i think it is either a or c.

Since line m is parallel to line n, this means that angle BDF = 30 degrees. The two angle BDF and DBA are alternate interior angles. They are congruent when m || n.

Now use the idea that angle CDE and angle EDF are supplementary (they add to 180 degrees)

(angle CDE) + (angle EDF) = 180
(angle CDE) + (30) = 180
(angle CDE) + 30 = 180
(angle CDE) + 30-30 = 180-30
angle CDE = 150 degrees

So therefore, the value of y is 150

This isn't one of the answer choices, but I noticed that 140 is listed twice. So it seems like there is a typo somewhere.