Call a is side of a square.

Give example a = 4. We have area S = a.a = 4.4 = 16.

Increase 20% to side we have S' = \(120\%a\cdot120\%a=23,04\)

Its area increases : \(\dfrac{23,04}{16}\cdot100\%=144\%-100\%=44\%\)

Choose D.