The circle and square gives the radius of the circle.
Square Area is 18, so square side is sqrt(18) = 3*sqrt(2)
Square diagonal is sqrt(2)*square side = 3*(sqrt(2))^2 = 6
Half square diagonal = circle radius = 3
Diagonal of Rectangle = diameter of circle = 6
Looking at one corner (¼) of the rectangle, it has diagonal = 3.
Call the short piece 'a'
Call the long piece 'b'.
Then a^2 + b^2 = 3 and (2a)*(2b) = 12 ==> a*b = 3