X : Y
1u + 27cm2 : 27cm2 + 4u
_____ 4u ____ 27cm2
/ \ / \
|---------------|--------|
|---------|--------------|
\__ ___/ \____ ___/
3u 81cm2
1u --> 81-27 = 54
Area of the square (X) --> 27 + 54 = 81 cm2
