2 - Draw Start & End Points of the arc circle wanted

Draw a circle ( by 3 points) by these 2 points then 100 as the third point in the Circle Radius clicked (up right corner)

then move rotate your circle by one of these points and rotate it to the second point
Delete not wanted part
(or any easy construction you want)
You have your arc circle radius 100 :)

Maybe not very orthodox but not other idea for the moment! :)