



 
Ivan, The area of the rectangular part is the width times the height so what remains to bee added is the area of the curved section. I expect the curve is part of a circle so the area can be seen as the area of the circle sector APBC minus the area of the triangle ABC. In my diagram Q is the midpoint of AB. Let h be the distance from Q to the top of the arch at P and b be the distance from A to Q. First I need to find the radius of the circle r. Triangle AQC is a right triangle Pythagoras theorem gives us
Simplifying and solving for r gives
Next I need the measure of the angle BCA. The tangent of the angle QCA is b/(r  h) and hence
The area of the sector APBC is a fraction of the area of the entire circle (π r^{2}) and the angle BCA is a fraction of 360^{o}. By the symmetry these fractions are the same, that is
and hence
The area of the triangle ABC is b(r  h) so finally
Thus measure b and h, use expression (*) to find r and then use expression (**) to find the area. I hope this helps,  


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