The Chocolate Squares

Here is a slab of chocolate, indented at the dotted lines so that the twenty squares can be easily separated. Make a copy of the slab in paper or cardboard and then try to cut it into nine pieces so that they will form four perfect squares all of exactly the same size.

Its source prints no answer for this problem, so there's nothing to check against.

H. E. Dudeney, Amusements in Mathematics (1917) · No. 149