The diagram shows a solid prism .

The trapezium , in which is parallel to , is a cross section of the prism.
The base of the prism is a horizontal plane.
and are rectangles.
The midpoint of is vertically above the midpoint of so that .
The perpendicular distance between edges and is 20 .
Calculate the size of the angle between and the plane . Give your answer correct to one decimal place.


