Answer:
140°
Explanation:
ArcDB is a curved piece of a circle. If you know the measures of the "central angles" (angles with their vertex at the center of the circle) then you can find the measure of the arc.
AngleAPB = 40°
AngleBPC = 90°
So AngleCPD must be equal to 50° see image.
ArcDB is equal to AngleBPD (90° + 50°)
ArcDB = 140°
see images.