Respuesta :

Answer:

x = 12

Step-by-step explanation:

The diagonals of a rectangle are congruent, thus

5x - 15 = 3x + 9 ( subtract 3x from both sides )

2x - 15 = 9 ( add 15 to both sides )

2x = 24 ( divide both sides by 2 )

x = 12