Respuesta :

Answer:

x = 6

Step-by-step explanation:

The perimeter is the sum of the 3 sides of the triangle. Sum the 3 sides and equate to 51, that is

15 + 5x - 6 + 2x = 51

7x + 9 = 51 ( subtract 9 from both sides )

7x = 42 ( divide both sides by 7 )

x = 6