To find a,construct a line that parallel to AB and DE cutting c, which you could refer to the photo((sorry for my terrible diagram ^^;;
from the photo,we can see that
a= <BCG + <GCE
<BCG=44° (alt.<, AB//FG)
<GCE=20° (alt<, FG//DE)
thus,a= 44°+20° =64°
hope it helps!
