Since quadrilateral ABCD is congruent to quadrilateral STUV, and STUV is a rectangle, the diagonals AC and BD of quadrilateral ABCD will be equal in length to the diagonals of rectangle STUV.
In a rectangle, the diagonals are equal in length and can be calculated using the Pythagorean theorem. For rectangle STUV, if diagonal SU = 5 cm, then the other diagonal TV will also be 5 cm because both diagonals of a rectangle are equal.
Since ABCD ≅ STUV, it follows that diagonals AC and BD will also be 5 cm.
Thus, according to the Transitive Property:
AC and BD = 5 cm.