Three Square Sudoku Problems

Triple-six

There are 19 convex tridominoes - omitting the 6x1 rectangle we get a set of 18 pieces which can be used to form three side 6 squares.

Triple-seven

If we combine a domino, a square and a 2x2 square we get a set of 21 pieces. These can form a 7x21 rectangle to form the basis of these problems.