Note that the side of each square is unity.
Along the horizontal, it has 3 complete squares, so the length of Henry's rectangle is 3 units,

Along the vertical, it has 2 complete squares while 1 half heighted rectangle, so the width of Henry's rectangle is,

Solve for the area of the rectangle as,

Thus, the Henry's rectangle is 3 units long, 2.5 units wide, and the area of the rectangle is 7.5 square units.