can anyone help?

Split green square in half; we have 2 identical rectangles. Rectangle's diagonal is the radius of the semi circle.

Ratio of rectangle's short side to long side is  1 : 2

The angle between the radius and the longer rectange side is     tan(A) = 1 / 2 = 26.56505118°

Let the radius  r = 1

Green square side    a = cos(A) = 0.894427191

Green  area          A_g = a² = 0.8 u²

Blue square diagonal is the radius and it is also  r = 1

Blue square side      b = sqrt(1/2) = 0.707106781

Blue  area              A_b = 2 * b² = 1 u²   

The ratio of the  green  area to the  blue  area is  4 : 5  

Hint:

Let the radius equal a set value. You can choose any number or numeral.    

Now work out the dimensions of the sides

etc

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