Hi Allison,

Please refer to Intro to arc measure you can watch the videos and learn how to solve this problem plus should you have further questions in the community there are peers will to answer the questions you have.

https://www.khanacademy.org/math/geometry/hs-geo-circles/hs-geo-arc-measures/v/intro-arc-measure

Thank you so much

hi alison

the arc ab is given 68 

and arc cabd we know it is 180 degrees 

now its also given that ab is parallel to cd

it means arcs CA and DB are equal

let CA be (x)

so now 68+ 2(x) = 180

2(x) =112

x=56

that is it 

THANKS so much!!