The whole shape is made up of a rectangle, two semicircles on $AB$
and on $DC$ together making one circle, and the two semicircles on
$AD$ and $BC$ making another circle.
Excellent solutions were sent in by a pupil from Dr Challoner's
Grammar School, Amersham
and Nisha Doshi ,Y9, The
Mount School, York. Here is one of their solutions: Take: $AB=2x,
AD=2y$.