Help solve this ellipse question?

A carpenter wishes to construct an elliptical table top from a sheet 4ft by 8 ft plywood to make a poker table for him and his buddies. He will trace out the ellipse using the “thumbtack and string” method as we saw in the video. What length of string should he use and how far apart should the tacks be located, if the ellipse is to be the largest possible that can be cut out of the plywood sheet?